12.5% is the same as 0.125, so is what you are asking equivalent to @-0.125@=8560?
If so, then I'll rewrite it as x-0.125x=8560 just for clarity (it is easier to read like that).
First, I would factor an x out of the left side.
Subtract 0.125 from 1
Divide both sides by 0.875.
8560/0.875 = 9782.85714
So your @ number is 9,782.85714. (If you round up at all, it won't work.)