Question 62375
All you need to do for variables like this is to just subract or add them to the other side.
Let me take you step by step with this one.

3x - 7 = 4x + 5
first lets put the variable on one side of the equation. lets do this by subtracting 3x from each side.
-7 = x + 5
then we want to get the variable by its self, so we subtract the 5 from each side of the equation
-13 = x

IF YOU DON'T GET IT STILL, JUST WRITE OUT "I NEED HELP WITH VARIABLES THAT ARE ON BOTH SIDES OF THE EQUATION" INSTEAD OF A PROBLEM, AND I OR SOMEONE ELSE WILL TRY TO HELP YOU.