Given data:
* The time taken by the box to hit the ground is 6.45 s.
* The initial velocity of the box is 15 m/s.
Solution:
By the kinematics equation, the height of the cliff is,
[tex]H=u_yt+\frac{1}{2}gt^2[/tex]where u_y is the vertical initial velocity of the box,
The vertical initial velocity of the box is zero,
Substituting the known values,
[tex]\begin{gathered} H=0+\frac{1}{2}\times9.8\times6.45\times6.45 \\ H=203.9\text{ m} \\ H\approx204\text{ m} \end{gathered}[/tex]Thus, the magnitude of the height of cliff is 204 meter.
Hence, the cliff was - 204 meter tall (measured in upward direction), and 1st option is the correct answer.