Table 14-12 bill's birdhouses costs revenues quantity produced total cost marginal cost quantity demanded price total revenue marginal revenue 0 $0 -- 0 $80 -- 1 $50 1 $80 2 $102 2 $80 3 $157 3 $80 4 $217 4 $80 5 $285 5 $80 6 $365 6 $80 7 $462 7 $80 8 $582 8 $80 refer to table 14-12. what is the marginal cost of the 5th unit