Answer :
The stone takes same time to go up to the top and to return from the top. Hence, the time to return or descend from the top is = t/2 seconds.
In this time the stone traveled on the descent:
s = 0 t/2 + 1/2 g (t/2)² = (g t²) / 8
In this time the stone traveled on the descent:
s = 0 t/2 + 1/2 g (t/2)² = (g t²) / 8