0 Required information Trey Monson starts a merchandising business on December 1 and enters into the following three inventory purchases. Also, on December 15, Monson sells 15 units for $20 each. Purchases on December 7 Purchases on December 14 Purchases on December 21 10 units @ $ 6.00 cost 20 units @ $12.00 cost 15 units @ $14.00 cost Required: Monson uses a perpetual inventory system. Determine the costs assigned to the December 31 ending inventory based on th method.