Hi!!
The answer is 9,00 watt-hours
Proofs:
24 hours in a day
The light bulb consumes 2400 watt-hours a day.
2400/24=100
Therefore: the light bulb consumes 100 watt-hours an hour.
3 days=72 hours
72+18=90
Therefore: 3 days and 18 hours=90 hours.
100*90=9,000
Therefore: a light bulb will consume 9,000 watt-hours in 3 days and 18 hours
