Answer:
D) Luigi should hire both workers as long as their marginal products do not change.
Step-by-step explanation:
As long as the employees' marginal revenue product equals or exceeds their marginal cost, they should be hired.
Marginal revenue product = marginal physical output x price per unit
The marginal cost for hiring both Jessie and Kathy is $80.
Jessie's marginal revenue product = 10 pizzas x $9 per pizza = $90 > $80
Kathy's marginal revenue product = 9 pizzas x $9 per pizza = $81 > $80