Widgeon Co. manufactures three products: Bales, Tales, and Wales. Their 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 Bales?
a. $7
b. $35
c. $5
d. $28