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 O decimal places, e.g. 5,275.) 4,500 windows Per Unit Sales Revenue 8775 $ 1.95 Variable Expenses Cost of Goods Sold 2925 0.65 Salaries Expense 950 Postage Expense 900 0.20 Total Variable Expenses v 4775 Contribution Margin V 4000 Fixed Expenses Advertising Expense 100 Salaries Expense 950 Insurance Expense 200 Total Fixed Expenses Operating Income $ 3400