Problem 12.18 LO 6 x e cel Activity level in units. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Variable costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fixed costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixed costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Total costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5,000 $10,000 30,000 20,000 $60,000 Production level, in units . . . . . . . . . . . . . . . . . . Variable costs . . . . . . . . . . . . . . . . . . . . . . . . . . Fixed costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixed costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . Total costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . February 12,000 $21,000 ? 18,000 $70,000 August 18,000 $ ? 31,000 ? $88,000 Required: a. Calculate the missing costs. b. Calculate the cost formula for mixed cost using the highlow method. c. Calculate the total cost that would be incurred for the production of 20,000 units. d. Identify the two key cost behavior assumptions made in the calculation of your answer to part c.