$A$ cylindrical tank is closed at both the ends by hemispheres. Its radius is $2.1 \,m$ and the total height is $9.2 \,m$. How many litres of petrol can it contain?

If the radius of a sphere is doubled,its volume becomes $\ldots \ldots \ldots$ times the volume of the original sphere.

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

$A$ drinking glass in the shape of a frustum of a cone has radii $3\,cm$ and $2\,cm$. If its height is $21\,cm$,its capacity is $\ldots \ldots \ldots cm^{3}$.

Metallic spheres of radii $6 \, cm$,$8 \, cm$,and $10 \, cm$,respectively,are melted to form a single solid sphere. Find the radius of the resulting sphere (in $cm$).

$16$ glass spheres,each of radius $2 \,cm$,are packed into a cuboidal box of internal dimensions $16 \,cm \times 8 \,cm \times 8 \,cm$. The box is then filled with water. Find the volume of water filled in the box (in $cm^3$).