$A$ village,having a population of $4000$,requires $150$ litres of water per head per day. It has a tank measuring $20 \,m \times 15 \,m \times 6 \,m$. For how many days will the water of this tank last?

Find the surface area of a sphere of diameter $14 \, cm$.
Assume $\pi = \frac{22}{7}$. (in $, cm^2$)

Mary wants to decorate her Christmas tree. She wants to place the tree on a wooden box covered with coloured paper with a picture of Santa Claus on it (see figure). She must know the exact quantity of paper to buy for this purpose. If the box has length,breadth,and height as $80 \, cm$,$40 \, cm$,and $20 \, cm$ respectively,how many square sheets of paper of side $40 \, cm$ would she require?

Twenty-seven solid iron spheres,each of radius $r$ and surface area $S$,are melted to form a single sphere with surface area $S^{\prime}$. Find the radius $r^{\prime}$ of the new sphere. (in $r$)

$A$ hemispherical bowl has a radius of $3.5\, cm$. What would be the volume of water it would contain (in $, cm^{3}$)?

Savitri had to make a model of a cylindrical kaleidoscope for her science project. She wanted to use chart paper to make the curved surface of the kaleidoscope (see figure). What would be the area of chart paper required by her,if she wanted to make a kaleidoscope of length $25\, cm$ with a $3.5\, cm$ radius (in $, cm^{2}$)? You may take $\pi=\frac{22}{7}$.