Question

you use 1500 watt hair heater for 3 hours. How many kilowatt -hours of electricity did you use?

Answer 1

1500 watt = 1.5 kilowatt

Now, energy = power * time
=1.5 * 3
4.5kilowatt-hour

Answer 2

1500 watt = 1500 * 10^-3
                 = 1.5 kilowatt
1.5 * 3 = 4.5 kilowatt hr