Answer:
a. Gross Profit =$89, Ending Inventory = $640
b. Gross Profit =$83, Ending Inventory = $631
c. Gross Profit =$86, Ending Inventory = $634
Explanation:
FIFO
<u>a.Gross Profit</u>
Sales ( 1 unit × $403)                      $403
Less Cost of Sales ( 1 unit × $314) ($314)
Gross Profit                                       $89 
<u>b. Ending Inventory</u>
Ending Inventory = Units Left × Earliest Price
                             = 2 units × $320
                             = $640
LIFO
<u>a.Gross Profit</u>
Sales ( 1 unit × $403)                        $403
Less Cost of Sales ( 1 unit × $320) ($320)
Gross Profit                                         $83 
<u>b. Ending Inventory</u>
Ending Inventory : 1 unit × $314 =  $314
                                1 unit × $317 =  $317
                               Total              =  $631
Weighted Average Cost method
<u>a.Gross Profit</u>
Sales ( 1 unit × $403)                      $403
Less Cost of Sales ( 1 unit × $317) ($317)
Gross Profit                                       $86 
<u>b. Ending Inventory</u>
Ending Inventory = Units Left × Average Price
                             = 2 units × $317
                             = $634