How much gasoline was consumed by the engine of a car that traveled 300 km at an average speed of 100 km / h

How much gasoline was consumed by the engine of a car that traveled 300 km at an average speed of 100 km / h, if the mechanical power of the engine is 46 kW? The engine efficiency is 36%.

Let’s determine the travel time:
300: 100 = 3 hours.
Engine perfect work:
46 * 3 * 3600 = 5 * 10 ^ 5 KJ
Then the heat of the burnt fuel:
q = 5 * 10 ^ 5 * 100/36 = 13.9 * 10 ^ 5 KJ
Heat of combustion q = Q * m where Q is the specific heat of combustion (4.6 10 ^ 7 J) then
m = q / Q = 13.9 * 10 ^ 8 / 4.6 * 10 ^ 7 = 30 kg.