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 4,500 Variable costs $ 9,900 Fixed costs 30,000 Mixed costs 21,580 Total costs $ 61,480 During October the activity level was 7,600 units, and the total costs incurred were $69,500. Required: a. Calculate the variable costs, fixed costs, and mixed costs incurred during October.