a piece of rubber tubing maintains a cylindrical shape as it is stretched. at the instant that the inner radius of the tube is 2 millimeters and the height is 20 millimeters, the inner radius is decreasing at the rate of 0.1 millimeter per second and the height is increasing at the rate of 3 millimeters per second. which of the following statements about the volume of the tube is true at this instant? (the volume