Scenario 12-14 If Farmer Brown Plants No Seeds on His Farm,he Gets

Scenario 12-14
If Farmer Brown plants no seeds on his farm,he gets no harvest.If he plants 1 bag of seeds,he gets 5 bushels of wheat.If he plants 2 bags,he gets 9 bushels.If he plants 3 bags,he gets 12 bushels.A bag of seeds costs $120,and seeds are his only cost.
-Refer to Scenario 12-14.Farmer Brown's marginal cost of producing 9 units of output (using 2 bags of seed) is

A) $240.
B) $120.
C) $40.
D) $30.