What is the area of a circular cushion with outer and inner radii of 3 cm and 2 cm respectively?
一个环形座垫，外圆与内圆半径分别为3厘米和2厘米，则环形座垫的面积为多少．
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

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

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<gadget id="calculator">28.26 - 12.56</gadget>
<output>15.7</output>

<result>15.7</result>