I need help solving this problem please...thanks

4x + 12 = 3x - 6 + 3x

4x + 12 = 6x - 6 (add the 3x's together)

12 = 2x - 6 (subtract 4x from both sides of equation)

18 = 2x (add 6 to both sides of equation)

9 = x (divide each side of equation by 2)