Cost function, account analysis, high-low method, average cost accuracy Following is cost data for the equipment maintenance department. This department charges other departments for the actual cost of materials and labor when making equipment repairs. The managers now want to develop a cost function that explains their overhead costs as a function of the number of service calls made each month. February March April May Salary-Manager $3,000 $3,000 $3,000 $3,200 Supplies 470 578 735 650 Insurance 200 200 250 250 Electricity 59 61 65 62 Property Tax 600 Repair Manuals 90 100 80 90 Total $3819 $3.939 $4.730 $4252 Service calls 90 110 140 125 "Salaries of all department heads are increased annually in May. "Insurance rates increased in April. *** Property taxes are paid in two equal installments in April and October A. Estimate the department's cost function using analysis at the account level. B. Using the cost function estimated in part (A), estimate the overhead cost for June if 135 service calls are expected, @ C. Calculate the average overhead cost per unit for the four-month period. Given this average cost, what is the estimated total cost for June? D. Which estimation method--the one in part (B) or part (C) is better? Why