If the radius of a circle increases from 3 cm to 5 cm, how much does its area increase?
一个圆的半径由3厘米增加到5厘米，它的面积增加了多少．
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">25 - 9</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<result>50.24</result>