A balloon rises vertically with a constant speed of 5ms−1. When the balloon is 60m above the ground, a stone A is dropped from it. One second after stone A is released, another stone B is thrown vertically upward from ground level with a speed of 20ms−1. Neglect air resistance.
(i) Obtain the time, measured from the instant stone B is thrown, after which the two stones meet.
(ii) Calculate the height above the ground at which the meeting takes place.