ring-shaped piece of iron has an inner diameter of 0.4 meters and an outer diameter of 0.6 meters. What is the area of the ring-shaped iron piece in square meters?
一个环形铁片，内圆直径是0.4米，外圆直径是0.6米，这个环形铁片面积是多少平方米？
<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">3.14 * 0.09</gadget>
<output>0.2826</output>

<gadget id="calculator">0.4 / 2</gadget>
<output>0.2</output>

<gadget id="calculator">0.2 ** 2</gadget>
<output>0.04</output>

<gadget id="calculator">3.14 * 0.04</gadget>
<output>0.1256</output>

<gadget id="calculator">0.2826 - 0.1256</gadget>
<output>0.157</output>

<result>0.157</result>