A circular piece of iron has an outer radius of 12 decimeters and an inner radius of 10 decimeters. What is its area?
一块环形铁片，外圆半径12分米，内圆半径10分米，它的面积是多少平方分米？
<gadget id="calculator">12 ** 2</gadget>
<output>144</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">144 - 100</gadget>
<output>44</output>

<gadget id="calculator">3.14 * 44</gadget>
<output>138.16</output>

<result>138.16</result>