Highlow method 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 highlow method to calculate the cost formula for mixed cost.