The height and the slant height of a cone are $21 \, cm$ and $28 \, cm$ respectively. Find the volume of the cone. (in $, cm^3$)

$A$ lead pencil consists of a cylinder of wood with a solid cylinder of graphite filled in the interior. The diameter of the pencil is $7 \,mm$ and the diameter of the graphite is $1 \,mm$. If the length of the pencil is $14 \,cm$,find the volume of the wood and that of the graphite. (in $,cm^3$)

What length of tarpaulin $3\, m$ wide will be required to make a conical tent of height $8\, m$ and base radius $6\, m$ (in $, m$)? Assume that the extra length of material that will be required for stitching margins and wastage in cutting is approximately $20\, cm$ (Use $\pi = 3.14$).

The front compound wall of a house is decorated by wooden spheres of diameter $21 \, cm,$ placed on small supports as shown in the figure. Eight such spheres are used for this purpose,and are to be painted silver. Each support is a cylinder of radius $1.5 \, cm$ and height $7 \, cm$ and is to be painted black. Find the cost of paint required if silver paint costs $25$ paise per $cm^2$ and black paint costs $5$ paise per $cm^2$.

Diameter of the base of a cone is $10.5\, cm$ and its slant height is $10\, cm$. Find its curved surface area. Assume $\pi = \frac{22}{7}$. (in $, cm^2$)

Find the surface area of a sphere with a diameter of $3.5 \, cm$. Assume $\pi = \frac{22}{7}$. (in $, cm^2$)