I can't seem to figure out the Dec 15th and Dec 21st cost per unit. Help please

1 Required information Required information Use the following information for the Quick Study below. (Algo) (11-14) [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 $40 each. PurchasesonDecember7PurchasesonDecember14PurchasesonDecember2110units@$26.00cost20units@$32.80cost15units$34.00cost OS 613 (Algo) Perpetual: Inventory costing with weighted average LO P1 Determine the costs assigned to ending inventory when costs are assigned based on the weighted average method. (Round your per unit costs to 2 decimal places.)