A claimant has the burden to prove by credible evidence to a reasonable degree of certainty both the fact of damages and the amount. Naden v. Johnson, 61 Wis. 2d 375, 387, 212 N.W.2d 585, 591 (1973). Although whether a party has sustained its burden of proof is a question of law, we must accept the trial court's assessment of the credibility of the witnesses. Burg v. Miniature Precision Components, 107 Wis. 2d 277, 287, 319 N.W.2d 921, 927. While damages for lost profits need not be proved with absolute certainty, a claimant must produce sufficient evidence so that a reasonable inference can be made as to the amount of damages. See Lindevig v. Dairy Equip. Co., 150 Wis. 2d 731, 740, 442 N.W.2d 504 (Ct. App. 1989).