Contribution Margin United Merchants Company sells 15,000 units at $40 per unit. Variable costs are $31.60 per unit, and fixed costs are $63,000. Determine (a) the contribution margin ratio, (b) the unit contribution margin, and (c) operating income. a. Contribution margin ratio (Enter as a whole number.) % b. Unit contribution margin (Round to the nearest cent. per unit c. Operating income