Since the stone is travelling, the displacement cannot be constant. This leaves the last 2 choices as possibilities. Now consider the acceleration that can act on the stone. Acceleration due to gravity is the only one. That means the horizontal component of the stone has to be constant since there is no acceleration in the horizontal direction.
Explanation:
It is given that,
The volume of a right circular cylindrical, 
We know that the volume of the cylinder is given by :

............(1)
The upper area is given by :



For maximum area, differentiate above equation wrt r such that, we get :



r = 1.83 m
Dividing equation (1) with r such that,



Hence, this is the required solution.
its c!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!