A circular pond has a diameter of 30 meters, find its area.
一个圆形池塘，它的直径是30米，求它的面积．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 ** 2</gadget>
<output>225</output>

<gadget id="calculator">3.14 * 225</gadget>
<output>706.5</output>

<result>706.5</result>