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 Variable costs Fixed costs Mixed costs Total costs 5,000 $11,000 31,000 15,320 $57,320 During October, the activity level was 9,400 units, and the total costs incurred were $68,500. Required: a. Calculate the variable costs, fixed costs, and mixed costs incurred during October. October Variable cost Fixed cost Mixed cost b. Use the high-low method to calculate the cost formula for mixed cost. (Do not round intermediate calculations and round your answers to 2 decimal places.) Cost formula per unit