I've always liked to do 0, 3, 12, 15 the points. So plug in 0, 3, 12, 15 separately to get y. The points are in parenthesis at the bottom.
2(0)-6y = 12
Y=-2 (0,-2)
2(3)-6y=12
-6y=6
Y=-1. (3,-1)
2(12)-6y = 12
24-6y = 12
-6y = -12
Y= 2. (12, 2)
2(15)-6y = 12
30-6y= 12
-6y=-18
Y = 3. (15,3)