$A$ hemispherical bowl made of brass has an inner diameter of $10.5 \, cm$. Find the cost of tin-plating it on the inside at the rate of $Rs. 16$ per $100 \, cm^2$.

The diameter of the moon is approximately one-fourth of the diameter of the earth. Find the ratio of their surface areas.

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?

The inner diameter of a circular well is $3.5\, m$. It is $10\, m$ deep. Find the cost of plastering this curved surface at the rate of $Rs. 40$ per $m^2$.

$A$ wall of length $10\, m$ was to be built across an open ground. The height of the wall is $4\, m$ and thickness of the wall is $24\, cm$. If this wall is to be built up with bricks whose dimensions are $24\, cm \times 12\, cm \times 8\, cm$,how many bricks would be required?

The diameter of a roller is $84\, cm$ and its length is $120\, cm$. It takes $500$ complete revolutions to move once over to level a playground. Find the area of the playground in $m^2$. $\left[\text{Assume } \pi = \frac{22}{7}\right]$ (in $, m^2$)