Under a modified wage plan, an employee earns $1.50 for each finished unit and is guaranteed $18 per hour as a minimum wage. If the daily quota is 96 units, on a particular day when an employee completes 90 units and works 8 hours, the amount of the make-up guarantee will be:
a. $27.00
b. $12.00
c. $9.00
d. $6.00