The circumference of a circle is 3.14 meters. If the radius of this circle is doubled, what is the circumference in meters?
一个圆的周长是3.14米，如果把这个圆的半径扩大2倍，周长应为多少米．
<gadget id="calculator">3.14 * 2</gadget>
<output>6.28</output>

<result>6.28</result>