Answer:98.4 m
Step-by-step explanation:
Given
Descending velocity of balloon(v)=5 m/s
velocity of stone relative to balloon(u)=7 m/s
thus u is the horizontal velocity of stone and v vertical velocity of balloon
time travel by stone to reach ground=4 s

where u=initial velocity
here u=5 m/s
t=4 s
a=g

horizontal distance traveled in this time


Thus stone at distance of 28 m from balloon
Also balloon and stone will be at same height at the time when rock hits ground