Whatever we do to one side of the equation, we have to do to the other side, so we subtract 65 from both sides so that we can isolate the variable.
3x + 65 - 65 = 7x + 13 - 65 : 3x = 7x - 52
Then we subtract 7x from both sides: 3x - 7x = 7x - 7x - 52
-4x = -52. Then we divide both sides by -4 to separate the 4 and the x.
-4x/-4 = -52/-4 : x = 13.
Hope this helps you!