The radius of the wheel of a toy car is 3 cm, how many centimeters does it roll once on the road?
一种玩具车车轮的半径是3厘米，它在路面上滚动一周，滚动了多少厘米．
<gadget id="calculator">3.14 * 3 * 2</gadget>
<output>18.84</output>

<result>18.84</result>