I was hoping someone could help me calculate the moment a tank wall experiences.

I have the following question:-

Tank contains water with dimensions:

4m Wide

12m Long

3m Tall

Determine the moment at the bottom of the long side at its centre.

I have drawn a sketch of the tank and highlighted in dark what I believe is the "bottom of the long side"

To calculate the force acting on the wall (12 x 3) I have done the following:-

F = p * g * a * y

p = density of water (1000)

g = gravity (9.81)

a = area (36)

y = distance from the top of the tank to the walls centroid (1.5)

1000 * 9.81 * 36 * 1.5 = 529740 N of force acting on the wall.

I am not really sure where to go from here?

Can anyone help?