Hi could anyone help with this? I can do part A but not part B.

A pebble is thrown vertically upwards from a point A with initial velocity 11.2 m/s

A) Find the greatest point above A that can be reached by pebble B

(I make it 6.4m)

The point B is 9m vertically above point A. At the same time that P was thrown from A, another pebble Q was thrown vertically downwards from B with initial velocity 0.8 m/s. The two pebbles collide after t seconds at a height h metres above point A.

B) Calculate the values of t and h

Not sure how to even start this bit :/

thanks