The diameter of a circular flower bed is 4m, what is its floor area in m**2.
一个圆形花坛的直径是4m，它的占地面积是多少m**2．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>