If the radius of the circle increases from 5cm to 9cm, how much does the area of the circle increase by πcm**2.
圆的半径由5cm增加到9cm，圆的面积增加了增加多少πcm**2．
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">81 - 25</gadget>
<output>56</output>

<result>56</result>