How much energy is used by an 80% efficient, 2 kW (input) motor running at a peak load for 5 hours?

Correct option is C

Rating of motor = 2 kW,
Time = 5 h
Efficiency = 80% = 0.8
η=(output power)/(input power)
Output power = 2×0.8 = 1.6 kW
So used energy =1.6×5 = 8kWh