The diameter of a circle is 20 cm, what is the area of the circle?
一个圆的直径是20厘米，这个圆的面积是多少．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<result>314</result>