$A$ metallic sphere of radius $21 \,cm$ is melted and recast to form a wire with diameter $0.5 \,cm$. Find the length of the wire in $m$.

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

The curved surface area of a cone with radius $12 \, cm$ and slant height $20 \, cm$ is ....... $\pi \, cm^2$.

$A$ metallic sphere with radius $42\, cm$ is melted to cast $8000$ identical balls. Find the radius of these balls (in $cm$).

$A$ pen stand made of wood is in the shape of a cuboid with four conical depressions and a cubical depression to hold the pens and pins,respectively. The dimensions of the cuboid are $10 \, cm$,$5 \, cm$,and $4 \, cm$. The radius of each of the conical depressions is $0.5 \, cm$ and the depth is $2.1 \, cm$. The edge of the cubical depression is $3 \, cm$. Find the volume of the wood in the entire stand. (in $, cm^3$)

The radius and the height of a cylinder are $28 \, cm$ and $54.5 \, cm$ respectively. It is closed at one end by a hemisphere and at the other end by a $21 \, cm$ high cone. Find the total surface area of the combined article. (in $cm^2$)