So let's say he was earring x before his raise. That means that:
x times 1.09 = 654 (1.09 represents 100% (this is the 1.0) of his original salary plus 9% (this is the .09) his raise.
So,
1.09x = 654; now divide both sides by 1.09 to isolate and solve for x, and you get x = $600.
