3x -6=6 get x by itself on one side.
to do this you have to add 6 to both sides (what you do to one side YOU ALWAYS DO TO THE OTHER)
3x = 12 now since x is being multiplied by 3 to undo that you divide it by 3 and since you did it to one side you do it to the other side
3x/3 = 12/3 3/3 is just 1
1x = 4
x = 4