There are 4 semi-circular gardens on each side of a square-shaped pond with each side 21 m. The cost of fencing the entire plot at the rate of Rs. 12.50 per metre is :

Length of the fence =$$4\pi R$$
Where, $$R = \frac{{21}}{2}m$$

$$\eqalign{ & 4\pi R \cr & = \left( {4 \times \frac{{22}}{7} \times \frac{{21}}{2}} \right)m \cr & = 132\,m \cr} $$
Cost of fencing :
$$\eqalign{ & = {\text{Rs}}{\text{.}}\left( {132 \times \frac{{25}}{2}} \right) \cr & = {\text{Rs}}{\text{.1650}} \cr} $$