There is a circular reservoir. Its circumference is about 31.4 meters, what is its footprint?
有一圆形蓄水池．它的周长约是31.4米，它的占地面积约多少？
<gadget id="calculator">31.4 / 2 / 3.14</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<result>78.5</result>