The diameter of the inner circle of a circular piece of iron is 6 cm, and the diameter of the outer circle is 8 cm. What is the area of this piece of iron in square centimeters?
一块环形铁片的内圆直径是6厘米，外圆直径是8厘米，这块铁片的面积是多少平方厘米？
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

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

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

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

<gadget id="calculator">16 - 9</gadget>
<output>7</output>

<gadget id="calculator">3.14 * 7</gadget>
<output>21.98</output>

<result>21.98</result>