A department of Delta Company incurred the following costs for the month of June. 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 $ 9,750

Fixed costs 32,000

Mixed costs 20,100

Total costs $ 61,850

During July, the activity level was 8,000 units, and the total costs incurred were $69,000.

Required:

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

b. Use the highlow method to calculate the cost formula for mixed cost.