Grandma Wang surrounded a semi-circular chicken farm with a fence against the wall. The total length of the fence is 15.7 meters. What is the area of the chicken farm in square meters?
王奶奶用篱笆靠墙围了一个半圆形的鸡场，篱笆的全长为15.7米，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>