If the radius of a circle increases by 2 centimeters, how many centimeters does its circumference increase?
一个圆的半径增加2厘米，则它的周长增加多少厘米．
<gadget id="calculator">2 + 2</gadget>
<output>4</output>

<gadget id="calculator">2 * 3.14 * 4</gadget>
<output>25.12</output>

<gadget id="calculator">2 * 3.14 * 2</gadget>
<output>12.56</output>

<gadget id="calculator">25.12 - 12.56</gadget>
<output>12.56</output>

<result>12.56</result>