Explanation:
The flat horizontal portion S is where the distance (y) does not increase or decrease. So Ted is stationary during this time frame.
In terms of speed, we would say speed = distance/time = (change in y)/(change in x). Note how this is the slope.
Rise = 0 because the horizontal line does not go up or down. The run is any positive number, though convention usually has Run = 1. Therefore, slope = rise/run = 0/1 = 0. All flat horizontal lines have a slope of 0 to indicate no upward or downward movement.