Uncle Wang surrounded a semicircular chicken farm with a 15.7-meter-long fence against the wall. What is the area of the chicken farm in square meters?
王大爷用15.7米长的篱笆靠墙围一个半圆形的养鸡场．这个养鸡场的面积是多少平方米．
<gadget id="calculator">15.7 / 3.14</gadget>
<output>5</output>

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

<gadget id="calculator">25 / 2</gadget>
<output>25/2 = around 12.5</output>

<gadget id="calculator">3.14 * (25/2)</gadget>
<output>39.25</output>

<result>39.25</result>