Remember the that the right side is positive and left side is negative so your starting at the midpoint i dont know how to explain it in words but look up some videos. its rise over run so for the left image u rise up 1 and u go over 2 so it will be 1 over 2 meaning 1/2. for the image on the right you go to the left(run) which is negative so its -1 up 3 cause u rise 3! its -1/3 i know its not the best explaining but I hope this helps!
