The diameter of a circle increases from 4 cm to 5 cm. How much has the circumference increased.
一个圆的直径由4厘米增加到5厘米．周长增加了多少．
<gadget id="calculator">3.14 * 5</gadget>
<output>15.7</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<gadget id="calculator">15.7 - 12.56</gadget>
<output>3.14</output>

<gadget id="calculator">3.14 / 12.56</gadget>
<output>0.25</output>

<result>0.25</result>