$A$ school provides milk to the students daily in cylindrical glasses of diameter $7\, cm$. If the glass is filled with milk up to a height of $12\, cm$, find how many litres of milk is needed to serve $1600$ students. (in $0.2$)

The dimensions of each iron hollow box are $30 \, cm \times 15 \, cm \times 10 \, cm$. What is the volume of a carton containing $60$ such boxes? (in $m^3$)

The radius of a sphere is $3.5\, cm$. Find the cost of plating gold on its surface at the rate of ₹ $150$ per $cm^{2}$. (in ₹)

The ratio of the surface area of a sphere to the curved surface area of a hemisphere is $9:2$. Find the ratio of their volumes.

Find the surface area of a sphere of diameter $49\, cm$ (in $cm^2$).

In $\Delta ABC$,$\angle B = 90^{\circ}$,$AB = 6.3 \, cm$,and $BC = 8.4 \, cm$. If the triangle is revolved about the side $AB$,find the volume of the cone so obtained. Similarly,if the triangle $ABC$ is revolved about the side $BC$,find the volume of the cone so obtained.