Two friends tossing balls from the main floor of a theatre to the balcony. One person stands exactly 4.0 m above the other person, and both release and catch the balls at the same height above their feet. the balls are always caught on their way down. The boy on the main floor releases his ball with an initial velocity of 25 m/s [up]. With what velocity should the girl on the balcony throw her ball at the same moment, so that both balls will be caught by the other person at exactly the same time?