3x +12 - x = 72
First, combine like terms. Let's add the 3x and the -x together.
3x-x+12 = 72
2x + 12 = 72
Now we will isolate the "x" by first subtracting 12 from each side of the equation.
2x + 12 - 12 = 72 - 12
2x + 0 = 60
2x = 60
Now to isolate the "x" and finally solve for x, divide both sides of the equation by 2
(2x/2) = 60/2
x = 30
So x = 30.
Let's check our work:
3x+ 12 - x = 3(30) + 12 - 30 = 90 + 12 - 30 = 102 - 30 = 72 which was exactly the other side of the original equation.