Answer:
2 seconds
Step-by-step explanation:
Given : 
To Find: after how many seconds it will hit the ground?
Solution:
The height of the balloon is given at time t : 
Now we re supposed to find after how many seconds it will hit the ground i.e. height will be 0 , h=0
Substitute h = 0 in the equation



Since the time cannot be negative
So, it will hit the ground after 2 seconds .