Hey guys.

Could you please guide me through this? I don't get it at all.

A ball is dropped from a lookout 180 m high. At the same time, a stone is fired vertically upwards from the valley floor with speed V m/s. Take g = $\displaystyle 10m/s^2$. Find for what values of V a collision in the air will occur. Find, in terms of V, the time and the height when collision occurs, and prove that the collision speed is V m/s. Find the value of V for which they collide halfway up the cliff and the time taken.