The internal and external diameter of a metallic hollow sphere are $6 \mathrm{cm}$ and $10 \mathrm{cm}$. By melting the sphere a solid cone of height $8 \mathrm{cm}$ is formed. What is the radius of base of the cone ?

There is some water in a cylindrical pot of diameter $8 \mathrm{cm}$. A solid iron sphere of diameter $6 \mathrm{cm}$ is completely immersed in water and water does not overflow. Find the increase of water level in $\mathrm{cm}$.

The edge of the wooden cube is $21 \mathrm{cm}$. Find the volume and surface area of a largest sphere that can be obtained from the wood.