Concord Window Cleaners' monthly income statement at several levels of activity is as follows: Windows washed 2,400 4,400 6,600 Sales revenue $3,696 $6,776 $10,164 Cost of goods sold 1,536 2,816 4,224 Gross profit Operating expenses 2,160 3,960 5,940 Advertising expense 540 540 540 Salaries and wages 740 940 1,160 expense Insurance expense 240 240 240 Postage expense 696 1,276 1,914 Total operating expense 2,216 2,996 3,854 Operating income $(56) $964 $2,086 (a) Identify each expense as fixed, variable, or mixed. Cost of goods sold Advertising expense Salaries and Wages expense Insurance expense Postage expense (b) Prepare a contribution margin income statement based on a volume of 5,400 Windows. e.g. 52.75 and all other answers to 0 decimal places, e.g. 5,275.) Sales Revenue Variable Expenses Cost of Goods Sold Salaries Expense Postage Expense : Total Variable Expenses Contribution Margin Fixed Expenses Advertising Expense Salaries Expense Insurance Expense Total Fixed Expenses Operating Income 5,400 windows Per Unit $ I