Use the following information to answer the following questions: Sellin rice er unit Variable ex ense per unit Fixed expenses $60,000 per month a. Operating income at a volume of 4,000 units per month is how many dollars? b. The break-even point in volume of units is how many units? c: The contribution margin ratio is what percent? d: If sales volume were to decrease by 10% from the original 4,000 unit volume, operating income would increase/decrease (input the word "increase" or "decrease") by how many dollars