If the cone is removed, the water level will change according to how the cylinder and cone were placed.
If it was like this,
Then all the water would fall off as the height of the cone and the water level are same.
If it is the upside down position of the above figure, then the water would fall according to the height of the cylinder
or cone is fully filled with water. the amount of water will be equal to the v of the the cone.
v of the cone= 1/3 pi*r*r*h
v of the cilinder=pi*r*r*h
water will rise by 4cms