Hey, I'm having trouble with this related rates Calculus problem. I just can't figure out a relationship between what's given and what I need to find. Here it is: A runner sprints around a circular track of radius 100m at a constant speed of 7 m/s. The runner's friend is standing at a distance 200m from the center of the track. How fast is the distance between the friends changing when the distance between them is 200m? Any help would be greatly appreciated!