balloon rises from rest with a constant acceleration g/8. A stone is released from it when it has risen to height  h. The time taken by the stone to reach the ground is

The velocity of balloon at height h, v=2g8hWhen the stone is released from this balloon, it will go upward with velocity v=gh2 (same as that of balloon). In this condition, time taken by stone to reach the ground ist=vg1+1+2ghv2=gh/2g1+1+2ghgh/4=2ghg=2hg