Use a 15.7-meter-long fence to enclose a largest semicircular sheepfold beside the fence. What is the area of the sheepfold in square meters?
用长15.7米篱笆，在围墙边围一个最大的半圆形羊圈．这个羊圈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>