Using solver to solve a real problem

I have just started using Mathcad, and i think it is a fantastic resource. I am trying to determine the moment capacity of a reinforced concrete beam. I have a number of equations that all depend on one another and need to solve for one of the variables. I have done this in excel using the goal seek function but i would prefer to use mathcad as it presents the results much better. I have tried to use a solve block with out any luck.

the basic theory is that some of the beam is in compression and the rest is in tension, I need to move the deviding line (the neutral axis) up or down until the forces balance, ie the sum of forces (compression and tension) are equal to zero.

I have attached the worksheet, if anyone can help i would realy appreciate it. I have highlighted the equations in yellow, they are at the bottom of the sheet.

Joe