b. Assume that more than one product is being sold in each of the following four case situations: (Enter "Contribution margin ratio" in percent. Round your final answers to the nearest whole dollar amount.) Case #1 Case #2 Case #3 Case #4 Sales $ 520,000 $ 420,000 $ 620,000 Variable expenses 273,000 434,000 Fixed expenses 105,000 136,000 Operating income (loss) $ 8,000 $ 26,000 $ (4,800) Average contribution margin (percentage) 20% 60%