A circular iron plate has an outer diameter of 0.4 meters and a ring width of 0.1 meters. What is the area of this circular iron plate in square meters?
一个环形铁片，外圆直径0.4米，环宽0.1米，这个环形铁片的面积是多少平方米．
<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">0.2 - 0.1</gadget>
<output>0.1</output>

<gadget id="calculator">0.1 ** 2</gadget>
<output>0.01</output>

<gadget id="calculator">0.04 - 0.01</gadget>
<output>0.03</output>

<gadget id="calculator">3.14 * 0.03</gadget>
<output>0.0942</output>

<result>0.0942</result>