don't know what I am doing wrong. please solve the whole thing correctly.

Required information [The following information applies to the questions displayed below.] 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 $20 each. If the units sold, eight are from the December 7 purchase and seven are from the December 14 purchase. Determine the costs ssigned to ending inventory when costs are assigned based on specific identification