First of all you need to make sure that each side has only letters and numbers, for this equation you first need to subtract 6 of each side, this way you can change the equation appearence without changing it's value, because if you do something in both sides of an equation, it's ok. After subtracting 6 of each side you can divide both sides for -4, this way you'll take only x in the left side and 12/-4 on the other, this way you will see that x = -3
