In a right circular conical tent $11$ persons can stay. Each person required $4 \mathrm{sq}. \mathrm{metre}$in the ground and the volume of air required is $20 \mathrm{c}. \mathrm{metre}$. What is the height of the tent for just $11$ persons. Write answer in $\mathrm{metres}$.

From an external point $P$, a tangent $PT$ is drawn to a circle with centre $O$. If $OP=13 \mathrm{cm}$ and $PT= 12 \mathrm{cm}$, then the radius of the circle is

Two circles touch externally. The distance between the centres of the circles is $13 \mathrm{cm}$. If the radius of one circle is $8 \mathrm{cm}$, then the radius of the other circle is

Numerical value of the curved surface of a sphere is equal to the numerical value of the volume. Then the diameter of the sphere is