4(x - 3) = 12
We move all terms to the left:
4(x - 3) - (12) = 0
Multiply
4x - 12 - 12 = 0
We add all the numbers and all the variables.
4x - 24 = 0
We move all terms containing x to the left hand side, all other terms to the right hand side
4x = 24
x= 24/4
x = 6