Concord Window Cleaners' monthly income statement at several levels of activity is as follows: 2,000 4,200 8,200 $ 3,900 $ 8,190 $ 15,990 1.400 2,940 5,740 2,500 5,250 10,250 Windows washed Sales revenue Cost of goods sold Gross profit Operating expenses Advertising expense Salaries and wages expense Insurance expense Postage expense Total operating expense Operating income 400 1,320 400 400 700 920 200 200 440 945 1,740 2,465 760 $ 2,785 $ 200 1,845 3,765 6,485 $ (a) Identify each expense as fixed, variable, or mixed. Cost of goods sold variable Advertising expense fixed Salaries and Wages expense mixed Insurance expense fixed Postage expense variable (b) Prepare a contribution margin income statement based on a volume of 6,400 windows. (Round unit cost to 2 decimal places, e.g. 52.75 and all other answers to 0 decimal places, e.g. 5,275.) 6,400 windows Per Unit Sales Revenue 12480 1.95 Variable Expenses : Cost of Goods Sold 4480 i 0.70 i Salaries Expense 500 0.16 Postage Expense 450 0.22 i Total Variable Expenses 6388 6388 Contribution Margin 6092 $ 6092 Fixed Expenses Advertising Expense 400 i Salaries Expense 500 i Insurance Expense 200 i Total Fixed Expenses 1350 Operating Income $ 4742