HOWE, Chief Justice:
INTRODUCTION
T 1 Petitioner Yeargin, Inc. seeks certiorari review of the court of appeals's decision upholding the Utah State Tax Commission's denial of Yeargin's sales tax refund claim. Yeargin, Inc. v. Tax Comm'n, 1999 UT App 094, 977 P.2d 527.
BACKGROUND
T2 In 1988, an ammonium perchlorate (AP) manufacturing facility owned by Pacific Engineering and Production Co. of Nevada (PEPCON) exploded and was destroyed. PEPCON Production Inc. (PPT), an affiliate of PEPCON, received financing to rebuild a similar facility near Cedar City, Utah, under the condition that PPI form Western Electrochemical Company (WECCO) to complete the construction of and subsequently operate the new facility. Upon formation, WECCO became the owner of the new facility, which began production of AP in August 1989.
T3 During construction, PPI and WECCO entered into an agreement with United Engineers and Constructors, Inc. (United) and its affiliate, Yeargin, wherein the parties agreed that
Contractor [United and Yeargin] shall perform, as necessary for completion of the Project, the detailed design and engineering (including preparation of plans, specifications, construction drawings, and estimates); shall procure, deliver and install permanent materials and equipment; shall procure and deliver construction equipment, supplies, tools; shall provide supervisory services and labor; and shall perform changes ... all in accordance with the terms of this Agreement.
This construction agreement also provided that
Title to all material and equipment procured by Contractor to be incorporated into the Project, shall pass to Owner [WECCO] upon delivery to common carrier or at the Project site, whichever is provided for in the purchase order.
T4 In or around May 1991, the Auditing Division of the Utah State Tax Commission (Division) conducted an audit of Yeargin, reviewing purchase orders, purchase order status reports, checks, ledgers, and sales tax returns for items purchased in connection with the AP project from October 1, 1988, through December 81, 1989. In September 1992, the Division sent Yeargin a statutory [290]*290notice claiming it owed $67,827.86 sales and use tax.1 Yeargin promptly paid the claimed tax amount to avoid further penalty and shortly thereafter filed a refund claim.
5 In April 1994, two years after Yeargin had paid the tax and filed a refund claim, and three years after the audit had commenced, the Division entered into a joint stipulation of fact2 with Yeargin and other entities involved in construction of the AP facility3 Paragraph twelve of the stipulation reads as follows:
During the course of construction of the facility PPI and WECCO entered into an agreement with United Engineers and Constructors, Inc., and its affiliate, Year-gin, for the purpose of providing assistance in the engineering, design and procurement for the construction of the AP manufacturing facility. United Engineers assisted WECCO in purchasing materials for use in 'the construction of the facility and located suppliers, obtained price quotations and arranged for WECCO to make purchases of materials. Title to all materials purchased for use at the WECCO facility passed directly to WECCO from the suppliers.
T6 After the Division denied Yeargin's refund claim, Yeargin filed a petition for redetermination with the Utah State Tax Commission (Commission), which heard the petition in a formal hearing in March 1997. Prior to the hearing, Yeargin submitted a filing entitled "Memorandum of Points and Authorities in Support of Motion in Limine," in which it asked the Commission to dismiss the matter and award its requested refund. Yeargin reasoned in the motion that because the parties stipulated that title to all goods passed to WECCO directly from the suppliers (as per paragraph twelve of the stipulation), Yeargin "never purchased for [its] own account materials nor held title to such materials," and thus could not be liable for the sales tax. Yeargin claimed to have relied upon the stipulation and argued that it "cannot now be simply abandoned as inconvenient by the Auditing Division."
T7 In its "Memorandum in Opposition to Petitioner's Motion in Limine," the Division asserted that the Commission should, in the interest of justice, relieve the parties from the binding effect of the stipulation. The Commission implicitly denied the motion in limine when it received evidence offered by the Division that Yeargin paid for certain materials used in the construction of the AP facility.
18 In its findings of fact, conclusions of law, and final decision, the Commission concluded, "based upon the evidence and testimony presented at the hearing," that Yeargin was indeed liable for the sales tax pursuant to section 59-12-103 of the Utah Code and rule 865-198-58 of the Utah Administrative Code as a purchaser or consumer of personal property. In particular, the Commission found:
During the course of construction of the facility, WECCO entered into an agreement with ... Yeargin, for purpose [sic] of providing assistance in the engineering, design and procurement for the construction of the AP manufacturing facility.... In addition to assisting WECCO, . Yeargin actually purchased some of the materials which were invoiced and billed to Yeargin and were paid for by checks from Yeargin. Yeargin ultimately installed those materials into the real property at the WECCO facility or consumed the materials in the construction process. The contract provides that title to all materials purchased for use at the WECCO facility would pass directly from suppliers to WECCO, but the invoices and checks indicate that some of the materials came to rest in the hands of Yeargin.
The Commission found paragraph twelve of the parties' stipulation to be ambiguous, and [291]*291thus received evidence that the parties intended for Yeargin to purchase some materials itself and not just assist in WECCO's purchasing.
T 9 The court of appeals concluded that the Commission was not arbitrary or unreasonable in finding that Yeargin, as a real property contractor, had installed or consumed the items for which the tax was due. The court also concluded that there was substantial evidence to support the Commission's finding that Yeargin was the final consumer of the materials and was thus liable for the sales tax pursuant to rule 865-198-58 of the Utah Administrative Code and section 59-12-103 of the Utah Code. See Yeargin, 1999 UT App 094 ¶¶ 15, 21-23, 977 P.2d 527. The court of appeals addressed paragraph twelve of the parties' stipulation in a footnote, finding that it applied only to the transactions in which Yeargin assisted WECCO in purchasing materials, not to the transactions "for which Yeargin issued purchase orders, received invoices, and issued checks." Id. at n. 7.
1 10 Yeargin seeks review of the court of appeals's decision, contending that the court erred in failing to address whether the Commission was bound by the facts agreed to by the parties in the stipulation, and if bound, whether the Commission erred in denying Yeargin's petition for redetermination.
STANDARD OF REVIEW
111 "On certiorari, we review the court of appeals'[s] decision for correctness." County Bd. of Equalization v. Stichting Mayflower Recreational Fonds, 2000 UT 57, ¶ 9, 6 P.3d 559. The court of appeals's decision is correct only if it accurately reviewed the Commission's decision under the appropriate standard of review. See Newspaper Agency Corp. v. Auditing Div., 938 P.2d 266, 267-68 (Utah 1997). Because the court of appeals was reviewing a formal adjudicative proceeding commenced before the Commission, the standard of review set out in section 59-1-610 of the Utah Code applies,. The court must review the Commission's findings of fact under a "substantial evidence" standard. See Utah Code Ann. § 59-1-610(1)(a) (1996). In other words, the court of appeals must uphold those findings of fact that are supported by substantial evidence, or "that quantum and quality of relevant evidence which is adequate to convince a reasonable mind to support a conclusion." Schmidt v. Utah State Tax Comm'n, 1999 UT 48, ¶ 7, 980 P.2d 690 (citations omitted). The court of appeals must review the Commission's conclusions of law for correctness. See § 59-1-610(1)(b).
ANALYSIS
I. JURISDICTION
{12 Before reaching the merits of this review, we address a jurisdictional issue raised by the Division.
113 The Commission issued its final decision on April 14, 1997. On May 7, 1997, Yeargin filed a petition for review by trial de novo in the third district court pursuant to section 59-1-601 of the Utah Code, which the legislature had amended in 1998 to provide that "beginning July 1, 1994, the district court shall have jurisdiction to review by trial de novo all decisions by the [tax] commission resulting from formal adjudicative proceedings." Utah Code Ann. § 59-1-601(1) (1996).4
14 While the case was pending in district court, we issued our decision in Evans & Sutherland in which we held that section 59-1-601 violated article XIII, section 11, of the Utah Constitution because it purported to confer upon the district courts a power expressly reserved in article XIII to the Commission.5 See Evans & Sutherland, 953 P.2d at 436.
[292]*292I 15 As a result of this decision, the district court was divested of jurisdiction over Year-gin's petition, and Yeargin therefore filed a petition for review with this court on November 6, 1997. We transferred the case to the court of appeals, which determined that the petition for review, though filed over six months after the filing deadline, was timely "[in light of the Supreme Court's treatment of the appellant in Evans and the fact that [Yeargin] would be left otherwise without an avenue for appeal in this matter."
¶16 The Division contends that the court of appeals improperly granted an "equitable exception" to the jurisdictional filing requirement because Yeargin's petition pending in the district court could have and should have been transferred from the district court to the supreme court pursuant to rule 44 of the Utah Rules of Appellate Procedure 6 and because the contours of the exception are ill-defined and potentially boundless.
{17 Yeargin responds that the court of appeals properly excepted this case based on our decision in Evans & Sutherland. We allowed the appellants in that case (and several others pending before us at the time) thirty days from our decision to refile their appeal 'with this court. See Evans & Sutherland, 953 P.2d at 443; see also Salt Lake City Corp. v. Property Tax Div. of the Utah State Tax Comm'n, 1999 UT 41, 979 P.2d 346; Hercules Inc. v. Auditing Div., 953 P.2d 445 (Utah 1997). Yeargin contends that because its petition for review was pending in the district court when Evans & Sutherland was issued, it was appropriately given the same thirty days to refile its petition with this court.
1 18 We agree with Yeargin and hold that the court of appeals appropriately granted Yeargin, a party whose petition for review was pending when we issued our decision in Evans & Sutherland, an "equitable exception" to the filing requirement. The Division's contention that we should rely on rule 44 because that rule gives an appellate court (ie., court of appeals or supreme court) the authority to transfer the improperly filed case to the appropriate court lacks merit. Rule 44 does not authorize a district court to transfer a case to an appellate court.7 Thus, without an equitable exception to the filing requirement, Yeargin, though timely filing a petition for review with a court having jurisdiction at the time the petition was filed, would have been without recourse through no fault of its own. We affirm the court of appeals's jurisdictional determination.
II. STIPULATION
119 We now address the legal question of whether the Commission was bound by the parties' stipulation of facts. We have held that "[olrdinarily, courts are bound by stipulations between parties," and that "parties are bound by their stipulations unless relieved therefrom by the court." First of Denver Mortgage Investors v. C.N. Zundel & Assocs., 600 P.2d 521, 527 (Utah 1979); see also Higley v. MeDonald, 685 P.2d 496, 499 (Utah 1984) (stating that stipulations conclusive and binding on parties); Dove v. Cude, 710 P2d 170, 171 (Utah 1985) (same). [293]*293Though these cases address the binding ef-feet of stipulations in judicial proceedings, we extend their applicability to stipulations in the context of administrative proceedings. We must now determine whether the stipulation at issue is still in effect, and if so, how it bears on the rights and obligations of the parties.
120 A stipulation of fact filed with and accepted by a court "acts as an estoppel upon the parties thereto and is conclusive of all matters necessarily included in the stipulation." Deseret Sav. Bank v. Walker, 78 Utah 241, 252, 2 P.2d 609 (1981). Such a stipulation "has all the binding effect of findings of fact and conclusions of law made by the court upon the evidence." United Factors v. T.C. Assocs., 21 Utah 2d 351, 354, 445 P.2d 766, 768 (1968). Because the facts stated in a stipulation are conclusive, a stipulation of fact "cannot be met by evidence tending to show that the facts are otherwise." Deseret Sav. Bank, 78 Utah at 252, 2 P.2d at 614. Thus, if the stipulation entered into by the parties still stands, the Commission and the parties are bound by it and the Commission cannot receive any evidence that conflicts with the facts contained in it.
121 Though " [there is an institutional hesitancy to relieve a party from a stipulation negotiated and entered into with the advice of counsel, " Rivera v. State Farm Mut. Auto. Ins. Co., 2000 UT 36, ¶ 11, 1 P.3d 539 (quoting Birch v. Birch, 771 P.2d 1114, 1116 (Utah Ct.App.1989)), a court has the discretion to set aside a stipulation under certain conditions. First, the party seeking relief from the stipulation must request it by motion from the trial court. See Fullmer v. Blood, 546 P.2d 606, 608-09 (Utah 1976) (holding that party was bound by stipulation of fact because it did not file motion with trial court requesting to be relieved from it); Deseret Sav. Bank, 78 Utah at 252, 2 P.2d 609 (stating that party must seek repudiation through direct proceeding). Second, the motion to repudiate the stipulation must be timely filed. See Klein v. Klein, 544 P.2d 472, 476 (Utah 1975). Third, it must show that the stipulation was "entered into inadvertently or for justifiable cause." First of Denver, 600 P.2d at 527 (emphasis added). Inadvertence cannot be the basis for repudiation when the mistake was " 'due to failure to exercise due diligence, [or if it could] have been avoided by the exercise of ordinary care."" Rivera, 2000 UT 36 at ¶ 11, 1 P.3d at 542 (citation omitted). We have also noted that "[iJt is unlikely that a stipulation signed by counsel and filed with the court was entered into inadvertently." Dove, 710 P.2d at 170. Fourth, the lower court must state its basis for relieving the parties of the stipulation. See id. ("In the absence of any articulated "justifiable cause,' we must reverse the withdrawal of the stipulation." (emphasis added) (quoting First of Denver, 600 P.2d at 527)).
122 In sum, to determine whether the Commission was bound to accept the facts as stated in the stipulation, and thus decide whether evidence tending to contradict those facts should have been excluded, we must determine whether the Division filed a timely motion requesting relief from the stipulation, and if so, whether the motion was granted based on "articulated 'Justifiable cause'" Id.
123 The Division did not file with the Commission a document entitled "Motion for Relief from Stipulation." However, in its "Memorandum in Opposition to Petitioner's Motion in Limine" {opposition memorandum) the Division asserted that the Commission, in the interest of justice, should relieve the parties from the stipulation because
At the time of the stipulation, counsel for the parties relied upon the representations of [Yeargin's counsel] in drafting and agreeing to paragraph 12 of the Joint Stipulation. Obviously, subsequent investigation showed the error should anyone interpret paragraph 12 to state that Yeargin Ine. had not purchased materials. To that extent, the Joint Stipulation reflects a mistake of fact.
«[ 24 We conclude that the Division's opposition memorandum, though not entitled such, was in substance a request to be relieved from the stipulation. See Armstrong Rubber Co. v. Bastian, 657 P.2d 1346, 1347-48 (Utah 1983) (holding that because pleadings are to be liberally construed, if the [294]*294nature of the motion is clear from its substance, an improper caption is not fatal); Howard v. Howard, 11 Utah 2d 149, 152, 356 P.2d 275, 276 (Utah 1960) (same). The Division made clear to the Commission its position on the stipulation and implicitly asked the Commission to set it aside. See Brunetti v. Mascaro, 854 P.2d 555, 558 (Utah Ct.App.1993) ("Because the ... documents clearly outlined the parties' respective positions on the question of withdrawal of the admissions, and the trial court was fully briefed thereon, it properly treated the various documents as a motion to withdraw the admissions."). Thus we hold that the Division did file a request to be relieved from the stipulation alleging that it was entered into under a mistake of fact.
125 However, we find that the Division's request was not timely filed, and thus the stipulation could not be withdrawn and was still in effect.8 We determined in Johnson v. Peoples Finance & Thrift Co., 2 Utah 2d 246, 272 P.2d 171 (1954), that a motion for relief from a stipulation "must be seasonably made." Id. at 250, 272 P.2d at 178. We concluded in that case that a motion to withdraw from a stipulation not made until over nine months after the stipulation was entered into did not entitle the movant to relief from the stipulation as a matter of law. See id. We have also found that motions filed five months, see Dove, 710 P.2d at 170, and ten months, see United Factors, 21 Utah 2d at 354, 445 P.2d at 769, after entering the stipulation did not entitle the movants to relief. We hesitate to relieve parties from a stipulation after such a duration because the longer a stipulation stands, the more likely a party is to have relied on it and the more likely it is that relieving the parties from it might prejudice the nonmoving party. See id. at 354-55, 445 P.2d at 769 (citing Johnson, 2 Utah 2d at 250, 272 P.2d at 173).
T26 The stipulation at issue in this case was entered into April 29, 1994, and was filed with the Commission May 5, 1994. On November 16, 1994, the Division received a copy of the construction agreement defining the relationship between Yeargin and WECCO. The Division asserts that it was not until receiving a copy of this agreement that it discovered the "error" in the stipulation. The Division did not file its "motion" to be relieved from the stipulation (opposition memorandum) until December 18, 1996, thirty-two months after the stipulation was entered, and nearly twenty-four months after it claims it was aware of the alleged mistake.
T27 Even were there justifiable cause to release the Division from the binding effect of the stipulation, the motion was so untimely that granting it would severely prejudice Yeargin. Yeargin relied on the stipulation for nearly three years. Bill Burke, in-house counsel for Yeargin from 1988-94, testified at the formal hearing that Yeargin made no attempt to preserve evidence to defend such an action as this because it considered the matter settled by the stipulation. In addition, very few, if any, of the people who had worked on the project still worked for Year-gin and thus could not provide testimonial evidence. We therefore hold that the motion to withdraw from the stipulation was filed untimely and that the stipulation is still binding on the parties and on the Commission.9
III. TAX LIABILITY
28 Having concluded that the stipulation is binding, we must now determine its effect on Yeargin's liability under the Utah sales tax statute.
129 Sales tax liability in Utah is governed by section 59-12-103 of the Utah Code, which provides in pertinent part: [295]*295"There is levied a tax on the purchaser for the amount paid or charged for the ... retail sales of tangible personal property made within the state[, and for] tangible personal property stored, used, or consumed in this state." Utah Code Ann. § 59-12-108(1)(a), - 108(1)(0) (1996). Utah Administrative Rule 865-19-58§ (1990) 10 was created as a guideline for imposing sales tax on materials and supplies sold specifically to owners, contractors, and repairmen of real property pursuant to sections 59-12-102 and 59-12-108. This rule provides:
A. Sale of tangible personal property to real property contractors and repairmen of real property is generally subject to tax.
1. The person who converts the personal property into real property is the consumer of the personal property since he is the last one to own it as personal property.
2. The contractor or repairman is the consumer of tangible personal property used to improve, alter or repair real property; regardless of the type of contract entered into-whether it is a lump sum, time and material, or a cost-plus contract.
Thus a contractor who is found to be a real property contractor is liable for sales tax on personal property he or she purchases or owns and converts into real property.11
130 We have defined a real property contractor as "one who purchases building materials for use in constructing homes, highways and the like." Chicago Bridge & Iron Co. v. State Tax Comm'n, 839 P.2d 303, 306 (Utah 1992) (emphasis added); see also Niederhauser Ornamental & Metal Works, Inc. v. Tax Comm'n, Auditing Div., 858 P.2d 1034, 1037 (Utah Ct.App.1993) (stating that a real property contractor is a contractor who purchases . and incorporates materials into real property). Real property contractors are considered ultimate consumers of the personal property because "their purchases of materi- . als that are incorporated into real property are the last transactions in which those materials can be subjected to the sales tax." Chicago, 839 P.2d at 306. And "sales tax is levied upon the ultimate consumer." Tummurru Trades, Inc. v. Utah State Tax Comm'n, 802 P.2d 715, 718 (Utah 1990).
131 Thus if Yeargin is a real property contractor, it is a final consumer and is liable for sales tax on the materials it purchased and converted into real property during construction of the AP facility. See Chicago, 839 P.2d at 806 ("[A] real property contractor is treated as a consumer for sales tax purposes."). Whether a contractor is a real property contractor for purposes of determining sales tax liability in Utah is a mixed question of law and fact. See Chicago, 839 P.2d 303 (Utah 1992) ("[Wlhether a taxpayer is a real property contractor or not is a ruling that is based in part on law and in part on fact.").12 To determine whether [296]*296Yeargin was a real property contractor on the AP project, we must determine whether it was a contractor that (1) converted materials it (2) purchased or owned into real property.
132 The Commission found that "Yeargin ultimately installed materials [it purchased] into the real property at the WECCO facility or consumed the materials in the construction process." The court of appeals upheld this finding because it was not unreasonable or arbitrary based on the relationship between Yeargin and WECCO as defined in the construction contract. That contract states: "Contractor [Yeargin] shall ... for completion of the Project ... deliver and install permanent materials and equipment." We affirm the court of appeals's conclusion that Yeargin converted material into real property because the construction contract, by providing that Yeargin would install permanent materials, constitutes substantial evidence of that fact.13
{33 The next issue we must address, and the one most disputed, is whether Yeargin purchased or owned any of the materials it converted into real property during the construction of the AP facility.
134 The Commission found that Yeargin purchased some of the materials it installed. In particular, the Commission found:
During the course of construction of the facility, WECCO entered into an agreement with ... Yeargin, for purpose [sic] of providing assistance in the engineering, design and procurement for the construction of the AP manufacturing facility.... In addition to assisting WECCO, . Yeargin actually purchased some of the materials which were invoiced and billed to Yeargin and were paid for by checks from Yeargin.
135 Yeargin contends that this finding is error because it is based on evidence that conflicts with the plain meaning of the stipulation. According to Yeargin, paragraph twelve of the stipulation "clear[ly] and unambiguous[ly]" shows the parties intended that WECCO, not Yeargin, purchase, own, and hold title to all materials used at the AP facility. Yeargin asserts that because the stipulation is clear, the evidence the Division adduced to show that Yeargin purchased or owned any materials was inadmissible. It contends that because the Commission relied on that evidence, and the court of appeals upheld its finding, the finding must be reversed.
T 36 If the evidence supporting the Commission's finding that Yeargin was a purchaser conflicts with the facts as stated in the stipulation, that evidence is inadmissible. See Deseret Sav. Bank, 78 Utah at 252, 2 P.2d 609 at 614 (stating that stipulation of facts "cannot be met by evidence tending to show that the facts are otherwise"). If the evidence is inadmissible and it is the only evidence offered to support the finding, the finding is not supported by substantial evidence and is thus erroneous. Whether the evidence conflicts with the facts as stated in the stipulation depends on the interpretation of the stipulation. We must therefore review the interpretation of the stipulation.
T37 The Commission implicitly concluded that the stipulation was ambiguous and thus looked at evidence other than its language to determine the parties' intent in entering into: it, It concluded:
[Alithough one of the functions of [Year-gin] was to assist WECCO, that does not foreclose the possibility that [Yeargin] may have itself purchased materials for the construction of the facility. [Yeargin]'s interpretation of paragraph 12 is one possible interpretation of the paragraph, but it is not the only possible interpretation.
T38 The court of appeals referred to the stipulation only in a footnote, stating:
As to those purchases that WECCO made, assisted in whatever way by Yeargin, the Stipulation's provision that title passed directly to WECCO would hold true. However, the Auditing Division presented substantial evidence that Yeargin also made [297]*297purchases on its own. We thus read the sentence governing passage of title as being dependent on the sentence immediately preceding it. That is, the provision that title passed directly to WECCO applies only to those transactions in which "[Year-gin] assisted WECCO in purchasing materials for use in the construction of the facility and ... arranged for WECCO to make purchases of materials," and does not apply to those transactions for which Yeargin issued purchase orders, received invoices, and issued checks.
1389 In reviewing the Commission's interpretation of the stipulation, we must determine first whether it correctly concluded that paragraph twelve of the stipulation is ambiguous. Because "'[al stipulation will be construed like other contracts or written instruments inter partes,'" Deseret Sav. Bank, 78 Utah at 251, 2 P.2d at 614 (quoting 20 Encyc. of Pleading and Practice, 657-58), whether it is ambiguous is a matter of law, which we review for correctness. See Willard Pease Oil & Gas Co. v. Pioneer Oil & Gas Co., 899 P.2d 766, 770 (Utah 1995). The test in Utah for determining whether a contract (and thus a stipulation) is ambiguous is found in Ward v. Intermountain Farmers Ass'n, 907 P.2d 264 (Utah 1995);
When determining whether a contract is ambiguous, any relevant evidence must be considered.... A judge should therefore consider any credible evidence offered to show the parties' intention.... If after considering such evidence the court determines that the interpretations contended for are reasonably supported by the language of the contract, then extrinsic evidence is admissible to clarify the ambiguous terms.... Conversely, if after considering such evidence, the court determines that the language of the contract is not ambiguous, then the parties' intentions must be determined solely from the language of the contract.
Id. at 268. In interpreting a stipulation of fact, the court must determine the intention of the parties at the time of stipulating. See id. (stating the court must " 'place itself in the same situation in which the parties found 2059 themselves at the time of contracting (quoting Pacific Gas & Elec. Co. v. G.W. Thomas Drayage & Rigging Co., 69 Cal.2d 33, 69 Cal.Rptr. 561, 442 P.2d 641, 645 (1968))). The only evidence relevant to that inquiry is evidence of the facts known to the parties at the time they entered the stipulation.
140 Under Ward, the Commission was correct in considering, to determine whether the stipulation was ambiguous, any relevant evidence adduced to support the parties' conflicting interpretations of it. See id. However, the evidence the Commission relied on to determine that the stipulation was ambiguous about Yeargin's status as a purchaser was not sufficient to support its conclusion.
T41 The Commission stated that its findings of fact and conclusions of law were based on the evidence and testimony presented at the final hearing. In particular, the finding that Yeargin was a purchaser of the materials it converted into real property was based on evidence that some of the materials installed into the real property or consumed in the process of construction were invoiced and billed to Yeargin and were paid for by checks from Yeargin. In addition, the Commission relied on the construction contract between the parties.
1 42 Because the construction contract had not been made available to the Division at the time the stipulation was entered into, it was not relevant, and thus was inadmissible, in the Commission's determination of the parties' intention at formation of the stipulation.
143 The only other evidence offered to support the Division's interpretation of the stipulation is the checks and invoices, which were discovered during the audit conducted sometime before the parties entered into the stipulation. Although both parties had access to this evidence at the time the stipulation was entered into, in light of the Division's admission that upon "further investigation" it discovered it had entered the stipulation in error, the checks and invoices are not relevant in determining the parties' intent upon entering into the stipulation and are thus inadmissible in determining wheth[298]*298er the stipulation is ambiguous.14 In other words, the Division stipulated to the fact that Yeargin was not a purchaser or an owner of materials but then discovered its mistake when it reviewed a copy of the construction contract.
144 We have determined that the evidence the Commission relied on to determine that paragraph twelve is ambiguous was not admissible. Because the Division submitted no other evidence to support its contention of ambiguity, we conclude that the language of paragraph twelve is not ambiguous. We therefore look to the language of that paragraph to determine whether the parties intended for Yeargin to purchase or own any of the materials used in constructing the facility. See Ward, 907 P.2d at 268 ([If after considering [evidence offered to support a particular interpretation], the court determines that the language of the contract is not ambiguous, then the parties' intentions must be determined solely from the language of the contract.").
1 45 Again, paragraph twelve reads:
During the course of construction of the facility PPI and WECCO entered into an agreement with United Engineers and Constructors, Inc., and its affiliate, Year-gin, for the purpose of providing assistance in the engineering, design and procurement for the construction of the AP manufacturing facility. United Engineers assisted WECCO in purchasing materials for use in the construction of the facility and located suppliers, obtained price quotations and arranged for WECCO to make purchases of materials. Title to all materials purchased for use at the WECCO facility passed directly to WECCO from the suppliers.
(Emphasis added.)
{46 We find the language stating that Yeargin "assisted" in and "arranged" for WECCO to purchase materials for construction of the facility clearly indicates Yeargin's and the Division's intentions that Yeargin not be a purchaser for its own account. In addition, the final sentence of paragraph twelve, providing that WECCO would take title to all materials purchased-not just the materials it purchased-unambiguously represents ' the parties' intent to indicate that WECCO, not Yeargin, owned all materials purchased for the project.
147 Because the stipulation stands for the fact that Yeargin did not own or purchase any materials for the facility, evidence cannot be admitted to contradict that fact. Thus Yeargin cannot be considered a real property contractor for purposes of sales tax liability.
¶48 In its brief, the Division asserts that because Yeargin presented invalid exemption certificates, it is lable for tax under two additional theories: as a vendor or as a retail consumer under the use tax. The court of appeals did not reach these questions, and we remand the case to that court, instructing it to make those determinations.
CONCLUSION
149 We hold that the Commission was bound by the facts as stated in the stipulation. Because the language of that stipulation clearly reflects that Yeargin and the Division agreed Yeargin was not a purchaser or owner of materials used in constructing the AP facility, the Commission's determination that Yeargin was a real property contractor was clearly erroneous. We therefore hold that Yeargin was not liable for sales tax as a real property contractor. We remand the case to the court of appeals for further determinations not inconsistent with this opinion.
I 50 DURHAM, J., MAUGHAN, and NEHRING, JJ., concur in HOWE'S, C.J. opinion.
1 51 Having disqualified themselves, Justice DURRANT and Justice WILKINS do not participate herein; District Judge Paul Maughan and District Judge Ronald E. Nehring sat.