In Zalk v. General Exploration Company (1980) 105 Cal. App. 3d 786, the plaintiff was retained to devote his exclusive time and attention to locating mining properties for the defendant's acquisitions. Plaintiff found one; defendant purchased it but refused to pay plaintiff's fee. The court determined plaintiff's finder's fee according to the Lehman formula, which gives 5 percent of the first million dollars of the purchase price, 4 percent of the second million, 3 percent of the third million, 2 percent of the fourth million and 1 percent of the remainder. ( Id. at p. 791, fn. 2.)