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

$A$ cubical box has each edge $10\, cm$ and another cuboidal box is $12.5\, cm$ long, $10\, cm$ wide and $8\, cm$ high. Which box has the smaller total surface area and by how much (in $ cm^2$)?

Find the cost of digging a cuboidal pit $8 \, m$ long,$6 \, m$ broad,and $3 \, m$ deep at the rate of $Rs. 30$ per $m^3$.

Twenty-seven solid iron spheres,each of radius $r$ and surface area $S$,are melted to form a single sphere with surface area $S^{\prime}$. Find the radius $r^{\prime}$ of the new sphere. (in $r$)

Find the volume of a sphere of radius $11.2 \, cm$. (in $, cm^3$)

The inner diameter of a cylindrical wooden pipe is $24 \, cm$ and its outer diameter is $28 \, cm$. The length of the pipe is $35 \, cm$. Find the mass of the pipe,if $1 \, cm^3$ of wood has a mass of $0.6 \, g$. (in $, kg$)