Trey Monson starts a merchandising business on December I and enters into the following three inventory purchases. Also, on December 15, Monson sells 15 units for $20 each. Purchases on December 7 10 units $ 6 cost Purchases on December 14 20 units @ $12 cost Purchases on December 21 15 units $14 cost Required Monson uses a perpetual inventory system. Determine the costs assigned to the December 31 ending inventory based on the FIFO method.