A circular grassy plot of land, 42 cm is diameter, has a path 3.5 m wide running around it outside. The cost of gravelling the path at Rs. 4 per square metre is :

Answer: Option C

Radius of the plot = 21 m
Area of the path :
$$\begin{array}{rl}& =\pi \left[{\left(24.5\right)}^2-{\left(21\right)}^2\right]m^2\\ & =\left[\pi \left(24.5+21\right)\left(24.5-21\right)\right]m^2\\ & =\left(\frac{22}{7}\times 45.5\times 3.5\right)m^2\\ & =500.5m^2\end{array}$$
∴ Cost of gravelling :
= Rs. (500.5 × 4)
= Rs. 2002