$CSA$ of a cylindrical tank with diameter $2.1 \, m$ and height $5 \, m$ is $\ldots \ldots \ldots \ldots \, m^2$.

$A$ metallic cone with radius $5 \, cm$ and height $8 \, cm$ is melted and recast to produce identical balls with diameter $0.5 \, cm$. Find the number of balls produced.

Two identical cubes each of volume $64 \, cm^{3}$ are joined together end to end. What is the surface area of the resulting cuboid? (in $cm^{2}$)

The radius of a hemispherical bowl is $9 \, cm$. It is completely filled with some medicine. If this medicine is filled in cylindrical bottles of diameter $3 \, cm$ and height $4 \, cm$,how many bottles can be filled?

The ratio of the radii of two spheres is $3:4$. Then,the ratio of their volumes is $\ldots \ldots \ldots$

The ratio of radii of two spheres is $2:3$. Then,the ratio of their volumes is $\ldots \ldots \ldots \ldots$.