Using parentheses here would make your post much clearer. I am assuming that you meant:
X^2 - 9x +20
-------------------- but this is not the only possible interpretation.
x^2 - 4x
Factoring, we get:
(x-4)(x-5)
---------------------
x (x-4)
Reduce this by cancelling the two (x-4) multipliers:
x-5
------ This is the final answer in most simplified form.
x