If the width of a ring is 3 cm, how much is the length of the inner circle less than the length of the outer circle?
一个圆环的环宽是3cm，那么内圆周长比外圆周长少多少cm．
<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">6 * 3.14</gadget>
<output>18.84</output>

<result>18.84</result>