Fluid Force. Help exam today

[tnutty]

A metal oil tank has cross-section that is a square rotated 45 degrees as shown in the figure above. Its height is 12 ft and width is 12 feet. The oil in the tank has a weight-density of 57 lb/ft3.
Write a definite integral that expresses the fluid force on the end of the tank when the oil is 4 feet deep?

Here is a link to the photo :
http://img17.imageshack.us/img17/2294/76984288.jpg [Broken]

hopefully you can make it out.

I am not sure how to set up the definite integral.

 

[minger]

Well, I think you can figure out out that
$$f = pA$$
Right?

Area is a function that you have. Pressure is a function as well. What are these functions?