how to solve 1/9 - 2/3x=1/18

Aziz,

2/3x and (2/3)x     are the same thing 

I think that you meant to say

I assume it should be (2/3)x and not 2/(3x)

I assume it should be (2/3)x and not 2/(3x).

To make life easier, multiply both sides by 18 to get rid of the 1/18 fraction.

Now, you end up with 18*(1/9) - 18*(2/3)x = 18*(1/18)...

You should be able to solve it from here...