Widgeon Co. manufactures three products: Bales, Tales, and Wales. The selling prices are $55, $78, and $32, respectively. The variable costs for each product are $20, $50, and $15, respectively. Each product must go through the same processing in a machine that is limited to 2,000 hours per month. Bales take 5 hours to process; Tales, 7 hours; and Wales 1 hour. What is the contribution margin per machine hour for Tales? a. $35 b. $7 c. $4 d. $28