How many balls with diameter $0.5\, cm$ can be produced by melting a metallic cylinder with radius $2\, cm$ and height $8\, cm$?

$A$ cylinder is closed at both the ends by $18\, cm$ high cones. The radius of the cylinder is $7\, cm$ and the total height of the solid is $64\, cm$. Find the volume of this solid (in $cm^3$).

The volume of the largest right circular cone that can be cut out from a cube of edge $4.2 \,cm$ is (in $cm^3$)

Total surface area of a hemisphere with diameter $2 \, cm$ is $\ldots \ldots \ldots cm^{2}$.

The slant height of a cone with radius $6 \, cm$ and height $8 \, cm$ is $\ldots \ldots \ldots \ldots cm$.

Water flows through a cylindrical pipe,whose inner radius is $1 \,cm$,at the rate of $80 \,cm/sec$ into an empty cylindrical tank,the radius of whose base is $40 \,cm$. What is the rise of water level in the tank in half an hour? (in $cm$)