Okay. Let's explain this. 960 per day. So let's start simple: 3 days and 960 per day is basically 2880 total watt-hours. Then we must do the 18 hours. How? We must multiply it the same way we did with the whole days. So we recognize that 18 hours is 18/24 hours in a day which is simplified: 18/24, 9/12, 3/4. So basically 18 hours is 3/4 of a day. So then we must multiply it by 3/4 of 960. So 960 x 3 = 2880, 2880 / 4 = 720. So then we must add them all up: 2880 + 720 = 3600 watt-hours in 3 days and 18 hours.
