I just wanna know where that 0.5 comes from?

A circular swimming pool has a diameter of 14 m, the sides are 4 m high, and the depth of the water is 3.5 m.?
How much work (in Joules) is required to pump all of the water over the side? (acceleration due to gravity 9.8 m/s^2 and density of water is 1000 kg/m^3)

Imagine the water is up to the brim.
The average work done in lifting up the whole water is = A h ρ g * [h/2] where A h ρ g is the mass of water of height h (= 4m).
Since there is no water up to a depth of 0.5m...

Question

I just wanna know where that 0.5 comes from?

A circular swimming pool has a diameter of 14 m, the sides are 4 m high, and the depth of the water is 3.5 m.?
How much work (in Joules) is required to pump all of the water over the side? (acceleration due to gravity 9.8 m/s^2 and density of water is 1000 kg/m^3)

Imagine the water is up to the brim.
The average work done in lifting up the whole water is = A h ρ g * [h/2] where A h ρ g is the mass of water of height h (= 4m).
Since there is no water up to a depth of 0.5m...