A truck has a minimum speed of 15mph in high gear. When traveling x mph, the truch burns diesel fuel at the rate of 0.0110469(1156/x + x) gal/mile. Assuming that the truch can not be driven over 54 mph and that diesel fuel costs $1.21 a gallon, find the following:

a. The steady speed that will minimize the cost of the fuel for a 620 mile trip.
(I got this, it was x=34)

b. The steady speed that will minimize the total cost of the trip if the driver is paid $20 an hour.

c. The steay speed that will minimize the total cost of a 650 mile trip if the driver is paid $28 an hour.

Question

A truck has a minimum speed of 15mph in high gear. When traveling x mph, the truch burns diesel fuel at the rate of 0.0110469(1156/x + x) gal/mile. Assuming that the truch can not be driven over 54 mph and that diesel fuel costs $1.21 a gallon, find the following:

a. The steady speed that will minimize the cost of the fuel for a 620 mile trip. 
(I got this, it was x=34)

b. The steady speed that will minimize the total cost of the trip if the driver is paid $20 an hour.

c. The steay speed that will minimize the total cost of a 650 mile trip if the driver is paid $28 an hour.