The volume of a sphere is equal to
So in order for us to know the increase in water level we need to know first the volume
The increase in height is equal to the volume of the sphere*3/base area of the cylinder.
Therefore the increase in height is
If you need the water level after the 3 balls were put just add 70/2=35 cm
then this would result to a height of 48 8/9 cm