Alice creates a machine that can shoot basketballs in a horizontal direction. Using a radar gun, Bob measures the speed of the basketball coming from the machine when it is stationary and finds that it is 30 km/hour. If Alice then puts the machine on top of a car, which she is driving at 50 km/hour toward Bob, and shoots a basketball in the direction of travel, what would be the horizontal speed of the ball as Bob measures it? (Neglect any effects of air resistance or other sources of friction.)