-3x+12=x-4
move x to the other side
sign changes from +x to -x
-3x-x+12=x-x-4
-3x-x=-4x ( combine like terms)
-4x+12=x-x-4
-4x+12=-4
move +12 to the other side
sign changes from +12 to -12
-4x+12-12=-4-12
-4x=-4-12
-4x=-16
divide both sides by -4 to get +x
-4x/-4=-16/-4
Cross out -4 and -4, divide by 4 . Then becomes -1*-1*x=x
divide by -4 for -16/-4
-16/-4=4
-4/-4=1
4*1=4
Answer:
x=4