Just simply using inverse operations and some commutative property of "addition". Addition and multplication properties of equality govern every step, other than some included commutativity properties. Answer by MathTherapy(10552) (Show Source): You can put this solution on YOUR website!
-12-x=8-3x
+x=8+x
-12=8-2x
-12=8-2x
-8 -8
___________
-20= -2x
-20/-2x
X= 10