Automate Goal Seek Function

I often find that the easiest way to automate these kinds of things is to solve them algebraically, then enter that formula into AA3. I have not been through the algebra thoroughly, but these usually simplify down to something like AA=(sum(a bunch of stuff)*G+sum(more stuff not related to G))/(G*(a different sum of stuff)). Even though G shows up in a few different places, these can usually be solved for G using basic algebra. If you need a refresher: http://www.purplemath.com/modules/solvelin3.htm shows some examples of algebra problems where the unkown x shows up in multiple places in the problem.

Review the algebra tutorial, because she has examples where x is on both sides of the equals sign. The usual first step in solving those is to move all of the like terms to the same side of the equation.

Here's how I usually reverse engineer algebra in a scenario like this (using the variable A to represent cell AA, other cells represented by column letter):

A=Z/H
Z=Y-X
H=G/1.2
Y=H=G/1.2
X=C+M+Q+R
M=K+L
L=0.1G
Q=0.019G
C,R,K are constants

Begin to substitute quantities into A

A=Z/H=(Y-X)/Y=(G/1.2-sum(C,M,Q,R))/(G/1.2)=(G/1.2-(C+K+0.1G+0.019G+R))/(G/1.2)
A=(G/1.2-C-K-0.1G-0.019G-R)/(G/1.2)
Continue by solving for G. First get G out of denominator by multiplying both sides by G/1.2, then combine like terms, and then finish solving for G.

Did I reverse engineer the formulas correctly? Are you able to solve for G from this point?