Solve Block - Iteration Problem

I am trying to solve a system of equations in the attached worksheet and having great difficulty. I am using the xd(, , ,) function to create a vector which is then passed to two definite integrals in order to find the area and centriod under a section of graph (not included).

The problem is that I have had to set the upper value of the xd function manually, I want to do it automatically.

The problem is a little clearer in the worksheet.

Mike