21. Hydro Corp. manufactures hydraulic pumps for use in small engines. Hydro uses two different independent variables (manufacturing time and machine hours) in two different equations to evaluate the Maintenance Cost. The most recent results of the two regressions are as follows: a. What does the r2 measure when used in regression analysis? b. Which of Hydro's cost driver's, Machine Hours or Set-ups, is best and why? Identify two reasons to support your choice of best cost driver. c. Using the cost driver you chose in part b., provide the cost estimation equation and estimate Maintenance Cost for the upcoming period. The Manufacturing Time is expected to be 5,000 and number of Machine Hours is projected to be 100. d. Give an important reason why regression analysis is preferred when estimating costs