But x is decreasing by 30 miles every hour. So we should say it's negative 30 miles per hour. So we know what y is. We know what x is. We know how fast y is changing, how fast x is changing with respect to time. So what we could try to do here is come up with a relationship between x, y, and s, and then differentiate that relationship with respect to time. And it seems like we have pretty much everything we need to solve for this.