Given that the time taken to reach the ground is t = 6 s
The final velocity is v = 0m/s
We have to find the height of the monument, h.
The initial velocity can be calculated by the formula

Here, g is the acceleration is due to gravity whose value is 9.81 m/s^2
Substituting the values, the initial velocity will be

The formula to find height is

Substituting the values, the height will be

Thus, the correct option is 177 m.