Answer:
Efficiency of the engine equals 20%
Step-by-step explanation:
We know that when the car moves it must do work against the resisting forces to keep moving and this work is spend as energy by the engine to keep the car moving.
we know that

Thus to keep the car moving for 100,000 meters the theoretical work that requires to be done equals

Now the actual energy spend by the car equals the energy spend by burning 2.8 gallons of gasoline.
Thus the energy produced by burning 2.8 gallons of gasoline equals

Thus the efficiency is calculated as
