The radii of two solid iron spheres are $1 \, cm$ and $6 \, cm$ respectively. $A$ hollow sphere is made by melting the two spheres. If the external radius of the hollow sphere is $9 \, cm$,then its thickness (in $cm$) is

Find the length of the canvas $2 \ m$ in width required to make a conical tent $12 \ m$ in diameter and $6.3 \ m$ in slant height (in $m$).

If the radius of a sphere is doubled,then its surface area is increased by (in $\%$)

$A$ rectangular block of metal has dimensions $21\, cm$, $77\, cm$, and $24\, cm$. The block is melted into a sphere. The radius of the sphere is .......... $cm$. (Take $\pi = \frac{22}{7}$)

The height of a right circular cone and the radius of its circular base are $9 \, cm$ and $3 \, cm$ respectively. The cone is cut by a plane parallel to its base so as to divide it into two parts. The volume of the frustum (i.e.,the lower part) of the cone is $44 \, cm^3$. The radius of the upper circular surface of the frustum $\left(\text{taking } \pi = \frac{22}{7}\right)$ is

$A$ tent is in the shape of a right circular cylinder up to a height of $3\, m$ and then becomes a right circular cone with a maximum height of $13.5\, m$ above the ground. If the radius of the base is $14\, m$,find the cost of painting the inner side of the tent at the rate of ₹ $2$ per $m^2$ (in ₹).