Concord Window Cleaners' monthly income statement at several levels of activity is as follows: Windows washed 2,000 4,500 7,500 Sales revenue $ 3,900 $ 8,775 $ 14,625 Cost of goods sold 1,300 2,925 4,875 Gross profit 2,600 5,850 9,750 Operating expenses Advertising expense 400 400 400 Salaries and wages expense 700 950 1,250 Insurance expense 200 200 200 Postage expense 400 900 1,500 Total operating expense 1,700 2,450 3,350 Operating income $ 900 $ 3,400 $ 6,400 (b) Prepare a contribution margin income statement based on a volume of 4,500 windows.(Round unit cost to 2 decimal places, e.g. 52.75 and all other answers to 0 decimal places, e.g. 5,275.) 4,500 windows Per Unit $ $ $ Advertising Expense Contribution Margin Cost of Goods Sold Fixed Expenses Insurance Expense Operating Income Postage Expense Salaries Expense Sales Revenue Total Fixed Expenses Total Variable Expenses Variable Expenses $