First of all, when you added 7 to both sides, you mistakenly changed 3/4x to 2/3x.
I am going to assume you meant to keep it as 3/4x.
Your equation is 3/4x = 2/3x + 15. Subtract 2/3x from both sides.
1/12x = 15. Multiply both sides by 12 to get x alone on one side.
x = 180
