For a circle with a radius of 2 decimeters, if the radius increases by 1 decimeter, how much does the circumference increase?
一个半径2分米的圆，如果半径增加1分米，那么周长增加多少分米．
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">2 * 3.14 * 3</gadget>
<output>18.84</output>

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

<gadget id="calculator">18.84 - 12.56</gadget>
<output>6.28</output>

<result>6.28</result>