You need to review how to handle "reversed differences":

The shortcut is



No doubt that is why you got the sign wrong.

Anyway, let's do your problem:





Multiply the bottoms only:



Have you learned the shortcut trick about reversed differences? 
That is, that (x-9) cancels into (9-x) and goes -1 times?
If you have, fine, then use it.  But if you haven't learned that
trick, then write 9-x in descending order -x+9 then factor out -1 
and get -1(x-9), like this:

Write 9-x in descending order as -x+9



Then factor -1 out of -x+9 which changes the signs:



Now you can cancel the (x-9)'s





Now you can substitute 9 for x:







Edwin