The table below shows the relationship between the number of times you get your car washed each month and your total monthly benefit from car washes. Each car wash costs $15.What is the marginal cost of the 5th car wash each month?

The table below shows the relationship between the number of times you get your car washed each month and your total monthly benefit from car washes. Each car wash costs $15.What is the marginal cost of the 5th car wash each month?

A.$14

B.$12

C.$4

D.$15

正确答案：$15