If the radius of a circle increases from 5 cm to 8 cm, how much does the area increase by π square centimeters square centimeters?
一个圆半径由5厘米增加到8厘米，面积增加了多少π平方厘米平方厘米．
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">64 - 25</gadget>
<output>39</output>

<result>39</result>