I should've maybe done a top view. Oh, here we go. This square represents the car, and it is moving in that direction. Now, they say at a certain instant, t sub zero. So let's draw that instant. So the first car is a distance x of t sub zero of 0.5 kilometers. So this distance right over here, let's just call this x of t, and let's call this distance right over here y of t. Now, how does the distance between the cars relate to x of t and y of t?