A department of Alpha Co. incurred the following costs for the month of September. Variable costs, and the variable portion of mixed costs, are a function of the number of units of activity:

Activity level in units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5,000

Variable costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $10,000

Fixed costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30,000

Mixed costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20,000

Total costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $60,000

During October the activity level was 8,000 units, and the total costs incurred were $70,500.

Required:

a. Calculate the variable costs, fixed costs, and mixed costs incurred during October.

b. Use the high–low method to calculate the cost formula for mixed cost.