The base of a cone with radius $7\, cm$ and height $24\, cm$ is hemispherical. Find the cost of painting its surface at the rate of ₹ $2/cm^2$. (in ₹)

Write 'True' or 'False' and justify your answer:
The curved surface area of a frustum of a cone is $\pi l(r_{1}+r_{2})$,where $l = \sqrt{h^{2}+(r_{1}+r_{2})^{2}}$,$r_{1}$ and $r_{2}$ are the radii of the two ends of the frustum,and $h$ is the vertical height.

$A$ metallic sphere of radius $21 \,cm$ is melted and recast into a wire with radius $0.5 \,cm$. Find the length of the wire in metres.

The volume of a cone with radius $5 \, cm$ and height $21 \, cm$ is $\ldots \ldots \ldots \, cm^{3}$.

The volume of a hemisphere is equal to:

Three metallic solid cubes whose edges are $3 \, cm$,$4 \, cm$,and $5 \, cm$ are melted and formed into a single cube. Find the edge of the cube so formed (in $cm$).