A circular machine part spacer has an outer radius of 3 cm and an inner radius of 1 cm. The area of this spacer?
一个环形的机器零件垫片，外半径是3厘米，内半径是1厘米．这个垫片的面积？
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

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

<gadget id="calculator">3.14 * 1</gadget>
<output>3.14</output>

<gadget id="calculator">28.26 - 3.14</gadget>
<output>25.12</output>

<result>25.12</result>