Harry owns a barber shop and charges $6 per haircut. By hiring one barber at $10 per hour, the shop can provide 24 haircuts per eight-hour day. By hiring a second barber at the same wage rate, the shop can now provide a total of 42 haircuts per day. The MRP of the second barber is
a. 18 haircuts.
b. $108.
c. 42 haircuts.
d. $126.