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