Find the volume of a sphere with radius $2.1 \, m$ (in $m^{3}$).

Twenty-seven solid iron spheres,each of radius $r$ and surface area $S$,are melted to form a single sphere with surface area $S'$. Find the ratio of $S$ to $S'$.

$A$ shopkeeper has one spherical laddoo of radius $5 \, cm$. With the same amount of material,how many laddoos of radius $2.5 \, cm$ can be made?

Find the volume of a sphere whose radius is $0.63 \, m$. Assume $\pi = \frac{22}{7}$. (in $, m^3$)

The diameter of a metallic ball is $4.2\, cm$. What is the mass of the ball,if the density of the metal is $8.9\, g/cm^3$ (in $, g$)?

$A$ metallic ball of radius $9 \,cm$ is melted and recast into three metallic balls. If the radii of two balls are $1 \,cm$ and $6 \,cm$,find the radius of the third ball (in $cm$).