Scenario 13-17 If Farmer Brown Plants No Seeds on His Farm, He

Scenario 13-17
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 13-17. 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.