The cross-section of a part is a ring, the radius of the outer ring is 0.5 meters, and the radius of the inner ring is 0.4 meters. What is the area of the cross-section of this part in square meters?
一种零件的横截面是一个圆环，外圈半径是0.5米，内圈半径是0.4米．这种零件横截面的面积是多少平方米？
<gadget id="calculator">0.5 ** 2</gadget>
<output>0.25</output>

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

<gadget id="calculator">0.25 - 0.16</gadget>
<output>0.09</output>

<gadget id="calculator">3.14 * 0.09</gadget>
<output>0.2826</output>

<result>0.2826</result>