To solve the problem we apply the motion kinematic equations as well as the techniques used to solve second order polynomial equations.
By definition we know that the height of a body is given by the function

As there is no initial speed or a distance previously traveled, the equation is:

Where,
g = Gravitational acceleration
t = time
h= Height
Rearranging to find the time we have,

Then, the sound of the splash take a time
to travel back, therefore, in time, it is necessary to adhere the new term, which converts the final time into:

If we make a similarity to the polynomial equation of the second degree where
we have to:

Solving to find x (which is equivalent to
) we have to:

Since the positive distance is what allows us to find the actual distance traveled we have finally to

The correct answer is B.