Windows washed 1,000 2,000 3,000 Sales revenue $3,000 $ 6,000 $ 9,000 Cost of goods sold 1,200 2,400 3,600 Gross profit 1,800 3,600 5,400 Operating expenses Advertising expense 400 400 400 Salaries and wages expense 700 900 1,100 Insurance expense 200 200 200 Postage expense 400 800 1,200 Total operating expense 1,700 2,300 2,900 Operating income $ 100 $ 1,300 $ 2,500 (a) Identify each expense fixed, variable, or mixed. Cost of goods sold Advertising Salaries and Wages Insurance Postage (b) Prepare a contribution margin income statement based on a volume of 2,500 windows. (Round unit cost to 2 decimal places, e.g. 52.75 and all other answers to 0 decimal places, e.g. 5,275.) 2,500 windows Per Unit . -> +