Stone A is dropped from rest from the top of an 80 m high cliff. Two seconds later, stone B is projected vertically upward from the foot of the cliff with a speed of 30 m s⁻¹. Take upward as positive and g = 9.8 m s⁻². At what height above the ground do the two stones cross each other?
a) 52m
b) 40m
c) 29m
d) 45m