Goal Seek or Simultaneous equation Help

[Jim May]

I'm trying to solve for this simultaneous equation,
And could use some help.. I think I need a function
In Cell D4 (****) to (in this case) bring back the 8.50%,
So that it will agree with my cell D9 (the 8.50%).
Any help appreciated..
Thanks in advance..

Contract Price $18,232.00 <linked cell
Cost (Equipment & Install) 9,313.90 <linked cell
Sub-total 8,918.10 < = D1-D2
S Comm s/b = the Row 18 ->> 10.00% << Input The ideal (Max) ****
Sales Commission (10% of CP) 1,823.20 < = D3*D4
Gross Margin - $$$'s $7,094.90 << = D3-D5
Gross Margin - % 38.91% << = D6/D1 <<< GP Using 10% Comm

Rate Determined according
to Rate Table - Opposite 8.50% << =VLOOKUP(D7,MyTableBelow,3,TRUE)


Lower Higher Down against
Limit Limit Base 10%
0.00% 29.99% 1.00%
30.00% 31.99% 2.50%
32.00% 33.99% 4.00%
34.00% 35.99% 5.50%
36.00% 37.99% 7.00%
38.00% 39.99% 8.50% << Current answer falls here
40.00% 10.00%

 

[Jim May]

I suppose (by now) that this task routine is not possible.
I think I need to consider a change in design, hummm..
Thanks to all who considered..