Power = 100W; Voltage = 240V; Time = 5 hours
Total energy used = Power x time = 100 x 5 = 500wh
converting to kwh, we have
5001000=0.5kWh×N5=N2.50\; \frac{500}{1000} = 0.5\text{kWh} \times \text{N}5 = \text{N}2.501000500=0.5kWh×N5=N2.50
