If the radius of a circle increases from 2cm to 4cm, how much does the area of the circle increase in c㎡
如果一个圆的半径由2cm增加到4cm，圆的面积就增加多少c㎡
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

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

<gadget id="calculator">16 - 4</gadget>
<output>12</output>

<gadget id="calculator">3.14 * 12</gadget>
<output>37.68</output>

<result>37.68</result>