A circular iron plate has an outer diameter of 0.8 meters and an inner diameter of 0.6 meters. What is the area of the iron plate in square meters?
一个环形铁片，外圆直径是0.8米，内圆直径为0.6米，铁片的面积是多少平方米．
<gadget id="calculator">0.8 / 2</gadget>
<output>0.4</output>

<gadget id="calculator">0.4 ** 2</gadget>
<output>0.16</output>

<gadget id="calculator">0.6 / 2</gadget>
<output>0.3</output>

<gadget id="calculator">0.3 ** 2</gadget>
<output>0.09</output>

<gadget id="calculator">0.16 - 0.09</gadget>
<output>0.07</output>

<gadget id="calculator">3.14 * 0.07</gadget>
<output>0.2198</output>

<result>0.2198</result>