The radius of a circle is 4 cm, what is the area of the circle?
一个圆的半径是4厘米，这个圆的面积是多少？
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<result>50.24</result>