There are two circles, big and small, the difference between their radii is 3 cm, what is the difference in cm between the circumferences of the two circles.
有大小两个圆，它们的半径之差是3cm，两个圆的周长之差是多少cm．
<gadget id="calculator">2 * 3.14 * 3</gadget>
<output>18.84</output>

<result>18.84</result>