The circumference of a semicircle is 30.84cm, find the area of the semicircle.
一个半圆的周长是30.84cm，求半圆的面积．
<gadget id="calculator">30.84 / 5.14</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>