Formula to find number that yields zero in another cell

Hello,

consider using Goal Seek instead of a formula.
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The algebra may be tedious for this, but it looks like it should be straightforward.

Working backwards:
1) put 0 in G28
2) G28=G26-G24. G26 is a constant, G24 is a function of x, so solve for G24 (Can we assume you can do the algebra?) and enter that formula into G24.
3a) G24=G18+G20+G21+G22 G20 and G21 are constants G22 is a function of G18, and G18 is a function of x.
3b) G22 is a function of G18 G22=constants*(G18+G20+G21)
3c) Substitute G22 into 3a, rearrange and solve for G18. Enter formula into G18.
4a) G18=G16+G14
4b) G16=constant*G14 substitute into 4a and solve for G14. Enter formula into G14
5) G14=G6+G8+G10+G11 G8 is the unknown, so solve for G8 and enter formula into G8.

I worked through that quickly, so be sure to check my algebra and thought process. I know the algebra is tedious, but that is the process I use to get the inverse of a function like this. If your algebra is rusty, this may help loosen those gears up: http://www.purplemath.com/modules/solvelin.htm Is that enough of a nudge, or do you need further assistance with the algebra here.