If 1 seed is 120$, and farmer may earn 2 bushels of wheat from 1 seed, then 5 bushels of wheat from 2 seed and 8 bushels of wheat from 3 seeds then the total cost is increasing in which of the following ways if there are no any fixed cost, a. increasing at an increasing rate, b. increasing at an constant rate, c. increasing at an decreasing rate, d. decreasing