The slope of a vertical line will always be undefined. The slope of a horizontal line is y = 0, because the line is not moving up or down. It is flat and constant. However, the slope of a vertical line is undefined because it has the same x-coordinate, and y = 0. This cannot happen because the slope will have a 0 in the denominator, causing it to be undefined.
7 yrds/sec because in the course of two seconds, he runs 14 yrds divide that by 2 to get 7 yrds/sec. you can allo chech with the next time which is 3 seconds more and he goes 21 yards more.
