Answer:
The time is 4.692 sec.
Explanation:
Given that,
Height 
Time t = 1.55 s
We know that,
The rate of change of height is the velocity.
So, the velocity is at t = 1.55 s


The velocity is upward with respect to the ground
We need to calculate the distance above the releasing point
Using equation of motion

Put the value into the formula



The height of the helicopter releases a small mailbag


We need to calculate the time
Using equation of motion

Put the value into the formula

On neglecting negative value of time
Hence, The time is 4.692 sec.