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 10 km/hour away from Bob, and shoots a basketball behind her and toward Bob, what would be the horizontal speed of the ball as Bob measures it, and which direction is it going? (Neglect any effects of air resistance or other sources of friction.)