remember you can do anything to an equation as long as you do it to both sides
[tex]\frac{9+x}{3x}=\frac{5}{6}[/tex]
multiply both sides by (3x)(6) (basically cross multiply)
(6)(9+x)=(5)(3x)
distribute
54+6x=15x
minus 6x both sides
54=9x
divide both sides by 9
6=x
x=6