Sam's Wholesale Bikes January 1 inventory balance 15 units at $350 per unit January 4 purchase 50 units at $375 per unit January 15 sale 40 units at $550 per unit February 8 purchase 80 units at $405 per unit February 15 sale 70 units at $550 per unit What is the gross margin for the two months assuming that Sam's uses the perpetual inventory weighted-average-cost method