Serene Dairy has four product lines: sour cream, ice cream, yogurt, and butter. The total cost of producing the milk base for the products is $45,000, which has been allocated based on the gallons of milk base used by each product. Results for July follow: Sour Cream Ice Cream Yogurt Butter Total Units sold 2,000 500 400 2,000 4,900 Revenue $10,000 $20,000 $10,000 $20,000 $60,000 Variable departmental costs 6,000 13,000 4,200 4,800 28,000 Fixed costs 5,000 2,000 3,000 7,000 17,000 Net income (loss) $ (1,000) 5,000 $2,800 $ 8,200 $15,000 How much are total joint costs of the products? Select one: O a. a. $28,000 O b. b. $17,000 O c. c. $45,000 O d. d. $15,000