It costs (12 + 0.008x) dollars per kilometre to operate a truck at x kilometres pet hour. In addition it costs $14.40 per hour to pay the driver.
What is the total cost per kilometre if the truck is driven at:
a) 40 km/h?
b) 64 km/h?

The cost consists of two component - the truck and the driver. The cost for the truck is given as 12 + 0.008x dollars per km. The cost for the driver is $14.40 per hour, and in one hour, the truck goes x kilometres, so the cost is $14.40/x dollars per km.