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 4,500 $ 8,100 32,000 20,680 $60,780 During October the activity level was 7,400 units, and the total costs incurred were $68,000. 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