The 3x and -3x combine to equal 0 thus disappearing from the right side. As you can see we moved the 3x to the left hand side by adding its opposite to both sides. Math Video How to Solve Equations with Variables on Both Sides.
Now you solve for one of the variables in terms of the other variable.
3x 9 Divide by 3 x 3. Subtraction property of equality. Add fifty three to both sides of the equation so that you get all constants on one side together. The example used in this video is 12x 3 5x 31.