#18. Samir owns a company that rents cars. When he employs 10 workers, his firm rents $20,000 worth of rentals in a day. When he employs 11 workers, total sales are $21,150. What is the value of the marginal product of the 11th worker?

a. $21,150

b. $2,115 ($21,150/10)

c. approximately $1923 ($21,150/11).

d. $1,150