To solve for x means to put x on one side, and everything else on the other side.
Let's do that:
[tex]-ax+4b\ \textgreater \ 9[/tex]
[tex]-ax \ \textgreater \ 9-4b[/tex]
And now we have to divide with -a.
Be careful: When dividing with anything that's negative, you have to reverse the inequality.
[tex]x \ \textless \ \frac{9-4b}{-a} [/tex]
Final solution:
[tex]x \ \textless \ \frac{4b-9}{a} [/tex]
