If the radius of a circle is increased from 3 decimeters to 5 decimeters, the circumference will increase by the same number of decimeters.
一个圆的半径由3分米增加到5分米，周长就增加多少分米．
<gadget id="calculator">3.14 * 5 * 2</gadget>
<output>31.4</output>

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

<gadget id="calculator">31.4 - 18.84</gadget>
<output>12.56</output>

<result>12.56</result>