How many spherical lead shots,each of diameter $4.2 \, cm$,can be obtained from a solid rectangular lead piece with dimensions $66 \, cm \times 42 \, cm \times 21 \, cm$?

$A$ metallic spherical shell of internal and external diameters $4 \, cm$ and $8 \, cm$,respectively,is melted and recast into the form of a cone of base diameter $8 \, cm$. The height of the cone is (in $cm$):

Twelve solid spheres of the same size are made by melting a solid metallic cylinder of base diameter $2 \, cm$ and height $16 \, cm$. The diameter of each sphere is (in $cm$):

The volume of a frustum of a cone is equal to $\ldots \ldots \ldots . .$

$A$ hemispherical tank full of water is emptied by a pipe at the rate of $3 \frac{4}{7}$ $litres$ per $second.$ How much time will it take to empty half the tank,if it is $3 \,m$ in $diameter?$ (in $minutes$) (Take $\pi=\frac{22}{7}$)

$A$ metallic sphere with radius $6 \, cm$ is melted and recast into a wire of radius $0.4 \, cm$. Find the length of the wire in metres.