A circular machine part has an outer radius of 3 cm and an inner radius of 2 cm. What is the area of this ring-shaped part?
一个圆环形的机器零件，外半径是3厘米，内半径是2厘米，这个环形零件的面积是多少．
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

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

<gadget id="calculator">9 - 4</gadget>
<output>5</output>

<gadget id="calculator">3.14 * 5</gadget>
<output>15.7</output>

<result>15.7</result>