If the outer radius of a circle is 6 decimeters and the inner radius is 4 decimeters, what is the area of the circle?
一个圆环外圆半径是6分米，内圆半径是4分米，圆环的面积是多少．
<gadget id="calculator">6 ** 2</gadget>
<output>36</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">36 - 16</gadget>
<output>20</output>

<gadget id="calculator">3.14 * 20</gadget>
<output>62.8</output>

<result>62.8</result>