A circular piece of iron, the radius of the outer circle is 5 cm, and the radius of the inner circle is 4 cm, what is the area of the iron piece in square centimeters (π≈3.14)
一个环形铁片，外圆的半径是5厘米，内圆的半径是4厘米，铁片的面积是多少平方厘米(π≈3.14)
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

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

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<result>28.26</result>