Answer:
X=0
Explanation:
I believe you meant 4x-9=3.5x-9, and I make this assumption due to it being impossible to "solve for x" in the format you gave. The only possibile solution to the question you gave is to simplify it, which would be 0.5x-18.
However, going with what I believe you meant, x would have to equal 0. There's no other possibility besides this, as 0 is the obvious option. Multiplecation by 0 will always produce 0. For 4x-9 AND 3.5x-9 to produce the same value, you'd have to make the variable a number that, when multipled by its coefficient, will produce an identical value. X=0 is the only number that fits this bill.