As you can see, the gaps between balls are continuously rising. Which means, ball is acted upon by gravitational force. If it is acted upon by force, that means ball is under acceleration. Ball is under free fall, so it is falling down at 9.8 m/s/s. The ball which is projectiled and the ball which was dropped will have same velocity in downward direction. i.e, downward component of velocity for both the balls will remain same so they will reach ground at the same. Horizontal component of velocity of right ball won't affect its downward motion.