Find the radius of a sphere whose surface area is $154 \, cm^2$. (in $, cm$)

$A$ right circular cylinder just encloses a sphere of radius $r$ (see figure). Find:
$(i)$ Surface area of the sphere,
$(ii)$ Curved surface area of the cylinder,
$(iii)$ Ratio of the areas obtained in $(i)$ and $(ii)$.

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

Monica has a piece of canvas whose area is $551 \, m^2$. She uses it to have a conical tent made,with a base radius of $7 \, m$. Assuming that all the stitching margins and the wastage incurred while cutting amounts to approximately $1 \, m^2$,find the volume of the tent that can be made with it. (in $, m^3$)

The radius of a spherical balloon increases from $7 \, cm$ to $14 \, cm$ as air is being pumped into it. Find the ratio of surface areas of the balloon in the two cases.

The volume of a right circular cone is $9856 \, cm^3$. If the diameter of the base is $28 \, cm$,find the height of the cone. (in $, cm$)