6x-3y=12 solve for Y, so try to get the y alone on one side of the equals sign...
subtract 6x so it would be 3y=12-6x now divide by 3 to get y alone ;)
3y divided by 3 is y and now for the other side
12-6x divided by 3 ... 12 would be 4 and -6 would be-2
so what you have left is y=4-2
simplify
y=2 :)