Look at your table. You labeled y1 and y2 where the x's are. y2 = 8, y1 = 4, x2 = 12 and x1 = 6. The slope then is (8-4)/(12-6) which is 4/6 or 2/3. You did run over rise instead of rise over run. Be careful. I see that a lot when I teach the concept to beginners.
