21. Car A and Car B leave an intersection at the same time. Car A travels North and Car B travels East. Four seconds later, Car A's position is 48 feet from the intersection and Car B's position is 20 feet from the intersection. If the speeds of Car A and Car B at that instant of time are 11 feet per second and 4 feet per second respectively, find the rate at which the distance between the two cars is changing at that instant of time. Set up a related rates problem and justify your solution. Round your solution to two decimal places and label it with appropriate units