What is CSA of sphere?

Find the total surface area of a hollow hemisphere whose outer and inner radii are $4.2$cm and $2.1$cm respectively

A sector containing an angle of 120 is cut off from a circle of radius 21 cm and folded into a cone. Find the curved surface area of cone. Take $\pi =\frac{22}{7}$

If the surface area of a sphere of diameter $14 \mathrm{c}\mathrm{m}$ is $k {\mathrm{cm}}^2$, then find the value of $k$. Use $\mathrm{\pi }=\frac{22}{7}$

A right circular cylinder just encloses a sphere of radius $r$. The surface area of the sphere is $K{\mathrm{\pi r}}^2$. Find $K$.

Find the surface area and volume of the sphere with radii $4 \mathrm{cm}$.  $(\mathrm{\pi }=3.14)$

Assume $\mathrm{\pi }=\frac{22}{7}$.  The diameter of a sphere is $21 \mathrm{c}\mathrm{m}$. If the surface area of the sphere is $k {\mathrm{cm}}^2$, then write the value of $k$ as final answer.

Match the following:

The surface area of a sphere is $616 {\mathrm{cm}}^2$. Find its radius. $(\text{Take} \mathrm{\pi }=22/7)$