You know the horisontal initial speed and also the vertical initial speed (which is 0). You know the constant of gravity (g=9.8 very likely, or it could be 10!). There are two separate problems -- that on horisontal and that on vertical. On the horisontal one, you have a speed and a time, so you could easily get the distance. On the vertical one, the initial speed is 0, the time is 3, the accel. is g, so you could find out the distance (that height of the cliff). Sorry for not separating the facts in here, but this answer is complete now.
