We are given:
Time period: 3 days and 18 hours
Energy consumed in given time period: 5400 watt-hours
Converting time to hours:
We know that one day is 24 hours
So, 3 days = 72 hours
Time period = 3 days + 18 hours
Time period = 72 hours + 18 hours
Time period = 90 hours
Converting to days
Time period = 3.75 days
Watt-hour consumption in a day:
Consumption = 5400 watt-hours / 3.75 days
Consumption = 1440 watt-hours/day