W/h is not a valid unit and is meaningless, although I understand the intent.
Energy = Power x Time
Power = Energy / Time
1 Watt is the rate of consumption of 1 Joule per second.
1 W = 1 J/s (one Joule per second).
Therefore 1 J = 1 Ws (1 Watt applied over 1 second).
This is how it’s done :
Energy = 7 W x 24 h/day x 5 days = 840 Wh
Energy = 840 Wh x 3600 s/h (seconds in one hour) = 3024000 J = 3 MJ (Mega Joules)
1 Wh is 3600 Joules since there are 3600 seconds in one hour.
Another way of doing the calculation is:
Energy = 7 J/s x 3600 s/h x 24 h/day x 5 days = 3024000 J
Energy = 3024000 J / 3600 J/Wh = 840 Wh
If your rate of consumption is 7 W, then the time to consume 840 Wh is : 840 Wh / 7 W = 120 h
To draw an analogy to water, think of Watts as Litres per second, and Watt-Seconds as Litres, and Watt-Hours as 3600 Litres.