If the surface area of a sphere of radius $r$ is decreased by $19\%$ and the radius of the new sphere is $r_1$, then find the ratio of $r_1$ to $r$

Find the total surface area of a hemisphere of diameter $10 cm$.

The curved surface area of a hemisphere with radius $7 \mathrm{cm}$ is: 

(Take$\mathrm{\pi }=\frac{22}{7}$)

The surface area of a sphere of radius $7 cm$ is

(Take $\pi =\frac{22}{7}$)

The radius of a semi-sphere is $7$ cm, find the total surface area of it.

If the volume of a sphere is $4851 {\mathrm{cm}}^3$, then its surface area (in ${\mathrm{cm}}^2$) is: (Take $\mathrm{\pi }=\frac{22}{7}$)