Uncle Li surrounded a circle with 15.7 meters long iron wire. What is the area of this circle?
李大伯用长是15.7米的铁丝围成一个圆，这个圆的面积是多少．
<gadget id="calculator">15.7 / 3.14 / 2</gadget>
<output>2.5</output>

<gadget id="calculator">2.5 ** 2</gadget>
<output>6.25</output>

<gadget id="calculator">6.25 * 3.14</gadget>
<output>19.625</output>

<result>19.625</result>