Hydrostatic Force Problem

Hey,

I've done an even problem from my book, and am not 100% sure if it's correct. It asks to find the Hydrostatic Force acting against an Area.

This figure represents a Dam. The top rectangle represents... I guess air? The is for height, at . The lower rectangle is the water. The half circle at the bottom is the Object will act as the area. The in the circle is the diameter of the half circle, which is . And last, but not least, represents the entire length of the Dam, which is .

To find the Hydrostatic Force, I did the following:

Did I correctly apply the concept? If so, is my Arithmetic correct also?

Thanks!