There are two circles, big and small. The radius of the big circle is 5 cm, and the radius of the small circle is 4 cm. The area of the small circle is equal to the area of the big circle.
有大小两个圆，大圆的半径是5厘米，小圆半径是4厘米，小圆面积是大圆面积的多少．
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<gadget id="calculator">16 / 78.5</gadget>
<output>0.203822</output>

<gadget id="calculator">3.14 * 0.203822</gadget>
<output>0.640001</output>

<result>0.640001</result>