Amber Baked Five Chocolate Cheesecakes

Amber baked five chocolate cheesecakes. When all costs, including implicit and external costs are included, the five cheesecakes cost her a total of $100. Producing a sixth cheesecake would increase these costs from $100 to $120. The smart choice for Amber is to produce the sixth cheesecake only if the benefits from the sixth cheesecake are more than

A) $25.
B) $20.
C) $24.
D) $120.
E) $30.