Aunt Zhang has built a circular chicken farm with a 31.4-meter-long fence. What is the area of the chicken farm in square meters?
张阿姨用31.4米长的篱笆围成一个圆形的养鸡场，这个养鸡场的面积是多少平方米？
<gadget id="calculator">31.4 / 3.14 / 2</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>