Suppose a car travels 108 km at a speed of 20.0 m/s, and uses 2.20 gallons of gasoline. Only 30% of the gasoline goes into useful work by the force that keeps the car moving at constant speed despite friction.

What is the force (in N) exerted to keep the car moving at constant speed?

If the required force is directly proportional to speed, how many gallons will be used to drive 108 km at a speed of 28.0 m/s?