Trey Monson starts a merchandising business on December 1 and enters into the following three inventory purchases. Monson uses a perpetual inventory system. Also, on December 15, Monson sells 15 units for $36 each. 10 units @ $22.00 cost Purchases on December 7 Purchases on December 14 Purchases on December 21 20 units @ $28.00 cost 15 units @ $30.00 cost Required: Determine the costs assigned to the December 31 ending inventory based on the FIFO method.