Explanation
To find the length of the fence to circle the arena, you need to compute for its circumference. The formula for circumference is:
\(\mathrm{C}=\pi \times diameter \)
\(C=3.14 \times 20=62.8\)feet
TIP: For a quick estimate, you can use pi = 3. In this problem, the answers given in the choices are quite far apart in value, so estimating will work fine. \(C=3 \times 20=60\), the closest number to 62.80 feet.