Answer:
It is impossible to 'lose' energy. It is simply transformed from one form to another. Maybe you could explain the question better? I had a question where I had to calculate the 'lost energy':
A 90% efficient 2 kW water heater is switched on for a period of 5 hours. The energy lost will be
a) 1kWh
b) 2kWh
c) 5kWh
d) 9kWh
If the heater is only 90% efficient, it will be using 1800 watts efficiently and wasting 200 watts per hour. 200 x 5 hours = 1000 watts.