of Minn.Stat. § 549.09, subd. 1(b), which presents a question of law that we review de novo. See, e.g., Hogenson v. Hogenson, 852 N.W.2d 266, 272 (Minn. App.2014); A&L Potato Co. v. Aggregate Indus., 759 N.W.2d 57, 58 (MinmApp. 2009); Duxbury v. Spex Feeds, Inc., 681 N.W.2d 380, 390-91 (Minn.App.2004), review denied (Minn. Aug. 25, 2004). Prejudgment interest begins to run when an action is brought or a written demand is made, whichever is first. Minn. Stat. § 549.09, subd. 1(b); see also Metalmasters of Minneapolis, Inc. v. Liberty Mut. Ins. Co., 461 N.W.2d 496, 502 (Minn.App.1990), review denied (Minn. Dec. 20, 1990). For the purpose of prejudgment interest, a settlement offer must remain open for 30 days. Minn.Stat. § 549.09, subd. 1(b); see also A & L Potato Co., 759 N.W.2d at 60 (<HOLDING>). The district court originally awarded
recognizing further that the offer of proof allows the aggrieved party to present a proper record for review on appeal and in the absence of such an offer error may not be preserved holding that a valid contract requires acceptance of an offer holding that an offer to donate cannot be an offer to sell holding that a valid settlement offer under section 54909 subd 1b  allows 30 days for the other party to accept an offer or make a counterclaim before the prejudgmentlimiting provisions of the statute are triggered holding an unaccepted settlement offer or offer of judgment does not moot a plaintiffs case emphasis added