A gardener wants to fence a circular garden of diameter 21 metre. Find the length and the cost of the fence required, if it costs Rs. 40 per metre and the gardener makes 2 rounds of fence.

Given diameter = 21 metre

Since we know that the diameter is twice the length of the radius.

So, radius $\mathbf{r}\mathbf{=}\frac{\mathbf{21}}{\mathbf{2}}\mathbf{ }\mathbf{metre}$

And, $\mathbf{Circumference}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{a}\mathbf{ }\mathbf{circle}\mathbf{=}\mathbf{2}\mathbf{\pi r}$

Substituting the values:

= $2\times \frac{22}{7}\times \frac{21}{2}$

$\mathrm{Circumference} \mathrm{of} \mathrm{circular} \mathrm{garden}=66 \mathrm{metre}$

Thus,  $\mathrm{Length} \mathrm{of} \mathrm{fence} \mathrm{for} \mathrm{two} \mathrm{rounds}=2\times 66$

Length of fence = 132 metre

Now, the given rate = Rs. 40 per metre

And we know that $\mathbf{Total}\mathbf{ }\mathbf{cost}\mathbf{ }\mathbf{=}\mathbf{ }\mathbf{Rate}\mathbf{\times }\mathbf{Circumference}$

= $\mathrm{Rs}. 40 \mathrm{per} \mathrm{metre}\times 132 \mathrm{metre}$

= Rs. 5280

Therefore, the length of the fence required is 132 meters, and the cost of the fence is Rs. 5280 for 2 rounds of fence.