The most important thing you need to remember about equations is that both sides must remain equal. You can make whatever you want, add, substract, divide, etc but you want to make it on both sides.
Now to "solve for x" means that we want to make the necessary operations in order to leave x alone.
In this case,
I put the numerator in parentheses so is more clear that the 2 divides the whole thing.
Now, on orther to isolate x, first we shoud get rid of the 2 dividing (3x-5)