Well, to think about that, let's first just think about what we're asking. So we're asking about the distance between the car and the truck. So right at this moment when the car is 0.8 miles from the intersection, the truck is 0.6 miles from the intersection, the truck is traveling at 30 miles per hour towards the intersection, the car is traveling 60 miles per hour towards the intersection, right at this moment, what is the rate at which this distance right over here is changing? And just so that we have some variables in place, let's call this distance s. So what we really are trying to figure out is right at this moment, what is ds dt going to be equal to? Well, let's think about what we know that we could use to somehow come to terms or figure out what ds dt is. Well, we know the distance of the car and the intersection. And let's just call that distance y.