Answer:
Weighted average: 
EI:            2,290
COGS:     9, 160
LIFO
EI:            2,400
COGS:     9,050
FIFO
EI:            3,000
COGS:     8,450
Explanation:
beginning 75 units at $ 18 = $  1,350
Mar. 15    200 units at $21 =  $ 4,200
Sept. 4    175 units at $24 =  $ 1,800
July 20   125 units at $22 =  $ 2,750
Dec. 2      50 units at $27 =  $ 1,350
total units:  625 units cost of goods available: 11,450
average cost: 11,450/625  =  $ 18.32 per unit
inventory units: 625 - 500 = 125 units
Weighted average: 
EI:          125 x $18.32 = 2,290
COGS: 500 x $18.32 = 9, 160
500 units were sold
LIFO:
last units are sold while frist are inventory
ending inventory
beginning 75 units at $ 18 = $  1,350
Mar. 15      50 units at $21 =  $<u>  1,050  </u>
                                    Total      2,400
COGS: available - ending inventory
11,450 - 2,400 = 9,050
FIFO
first units are sold while last are inventory
Dec. 2      50 units at $27 =  $ 1,350
July 20     75 units at $22 =  $ <u>1,650   </u>
                                    Total      3,000
COGS: available - ending inventory
11,450 - 3,000 = 8,450