Solving Fluid Static Problem with Parallelepipeds

[badruk]

Homework Statement

There are 2 parallelepiped with dimension x,l,h those were united to create a bigger solid with an "L" form ( see the picture ). The solid is isolated and full of water.
What's the force that must be done against the top wall, to make the system in equilibrium?

Here's the image:

Homework Equations

Pascal's principle: everywhere the pressure's the same
Pressure at the bottom: $P=P_ext+\rho gh$

The Attempt at a Solution

The external pressure is 0 because the system is isolated; so I thought that the pressure against the wall may be $P=\rho g h$ and the Force would have been ( modular ) $|F|= \rho g h \times S $ where S is the section of the wall.. Unlucky this is not the right answer..

May someone help me?

 

[Spinnor]

I think I know this stuff and would try to help but the problem is not clear to me as stated. If you can make an attempt at being more clear I will give it another shot.