please can you explain the answer step by step? thx

Trey Monson starts a merchandising business on December 1 and enters into the following three inventory purchases; Purchases on December 7 Purchases on December 14 Purchases on December 21 18 units @ $4.00 cost 35 units @ $6.00 cost 28 units @ $7.00 cost Monson sells 28 units for $10 each on December 15. Monson uses a perpetual inventory system. Determine the costs assigned to ending inventory when costs are assigned based on the weighted average method. (Round you per unit costs to 2 decimal places.)