\f7. The marginal cost of hiring the 91th worker isl a) $350 b) $40 c) $0 (1) $50 8. If hiring the 9'3l1 worker increases total productivity by 12 units and the sales price of each unit is $3, a) the rm should not hire the 9'11 worker b) marginal revenue equals $36 c) the rm should hire the 9th worker (I) a) and b) are both correct