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 benefit of the 3rd 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 benefit of the 3rd car wash each month?
A.$4
B.$12
C.$48
D.$16
正确答案：$12