15. A point is moving on the graphofxy= 36. When the point is at (4, 9), itsxcoordinate is increasing by 4 units per second. How fast istheycoordinate changing at that moment?

17. A boat is being pulled toward a dock as shown in the figure.I fthe rope is being pulled in at 3 feet per second, how fast is the distance between the dock and the boat decreasing when it is 30 feet from the dock?

19. A rock thrown into a still pond causes a circular ripple.Ifthe radius of the ripple is increasing by 2 feet per second, how fast is the area changing when the radius is 10 feet?