Bargain Rental Car offers rental cars in an off-airport location near a major tourist destination in California. Management would like to better understand the variable and fixed portions of it car washing costs. The company operates its own car wash facility in which each rental car that is returned is thoroughly cleaned before being released for rental to another customer. Management believes that the variable portion of its car washing costs relates to the number of rental returns. Accordingly, the following data have been compiled:

Month Rental Returns Car Wash Costs
January 2,300 $ 10,400
February 2,500 $ 12,800
March 2,700 $ 11,200
April 2,900 $ 13,400
May 3,600 $ 15,600
June 4,900 $ 22,100
July 5,500 $ 21,600
August 5,300 $ 20,700
September 4,700 $ 22,200
October 3,800 $ 19,300
November 2,100 $ 10,100
December 2,600 $ 12,100

Using least-squares regression, estimate the variable cost per rental return and the monthly fixed cost incurred to wash cars.

a. What is fixed cost per month?

b. what is variable per rental return?