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 26 units for $25 each. Purchases on December 7 16 units @ $10.00 cost Purchases on December 14 33 units @ $15.00 cost Purchases on December 21 26 units @ $18.00 cost.