The radius and height of a circular cylinder are changing with time in such a way that the volume remains constant at 1 liter (= 1000 cubic centimeters). If, at a certain time, the radius is 4 centimeters and is increasing at the rate of 1/2 = 0.5 centimeter per second, what is the rate of change of the height? The volume of a cylinder with radius r and height h is equal to rh. Remember to apply appropriate units for the variables you use.