Hydrostatic Force Problem!!!

A large tank is designed with vertical ends in the shape of the region between the curves y = x^2/2 and y = 13, measured in feet. Find the hydrostatic force on one end of the tank if it is filled to a depth of 8 ft with gasoline. (Assume the gasoline's density is 42.0 lb/ft^3

Sooo, I am not sure what I'm dealing with, but I think we are integrating from 0 to 8 and pull out the 42 of the integral, of something, I think the curves are confusing me. I know that hydrostatic force is area*pressure, and I think the pressure is 42 times x. But I don't know what the area is. Please help!