The perimeter of a semicircular lawn is 30.84 meters, what is the area of the lawn in square meters?
一个半圆形草坪的周长是30.84米，这个草坪的面积是多少平方米？
<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">6 ** 2</gadget>
<output>36</output>

<gadget id="calculator">36 / 2</gadget>
<output>18</output>

<gadget id="calculator">3.14 * 18</gadget>
<output>56.52</output>

<result>56.52</result>