At a certain instant, t sub zero, the first car is a distance x sub t sub zero, or x of t sub zero, of half a kilometer from the intersection, and the second car is a distance y of t sub zero of 1.2 kilometers from the intersection. What is the rate of change of the distance, d of t, between the cars at that instant, so at t sub zero? Which equation should be used to solve the problem? And they give us a choice of four equations right over here. So you could pause the video and try to work through it on your own, but I'm about to do it as well. So let's just draw what's going on. That's always a healthy thing to do.