Romeo is throwing pebbles gently up to Juliet's window, and he wants the pebbles to hit the

Question:

Romeo is throwing pebbles gently up to Juliet's window, and he wants the pebbles to hit the window with only a horizontal component of velocity. He is standing at the edge of a rose garden 8.0 m below her window and 8.5m from the base of the wall (Fig. 3-49). How fast are the pebbles going when they hit her window?