Let's first distribute the -6 on the right side of the equation:

12 - 3x = 18 - 6x - 12

Next, let's combine like terms on the right side:

12 - 3x = 6 - 6x

Now, let's isolate x on one side of the equation. Add 3x to both sides:

12 = 6 + 3x - 6x

12 = 6 - 3x

Subtract 6 from both sides:

6 = -3x

Divide both sides by -3 to solve for x:

x = -2

Therefore, the solution to the equation is x = -2.