Using a perpetual system, how do I determine the FIFO,LIFO, weighted average, and specific identification.

Question

Dec. 7, 10 units @ 6.00, Dec 14 20units @ 12.00, and Dec 21. 15 units @ 14.00 cost. trader sells 15 units for 25 each on December 15. Eight of the sold units are from the Dec purchase and seven are from the Dec 14 purchase. Trader uses a perpetual inventory system. Determine the costs assigned to the Dec. 31 ending inventory when costs are assigned.