Restate the following income statement for a retailer in contribution format. Sales revenue ($100 per unit) $ 84,000 Less cost of goods sold ($56 per unit) 47,040 Gross margin 36,960 Less operating costs: Commissions expense ($7 per unit) $ 5,880 Salaries expense 7,800 Advertising expense 5,800 Shipping expense ($1 per unit) 840 20,320 Operating income $ 16,640