A circular machine part gasket with an outer radius of 3 cm and an inner radius of 1.5 cm. What is 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1.5厘米．这个垫片的面积是多少？
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

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

<gadget id="calculator">1.5 ** 2</gadget>
<output>2.25</output>

<gadget id="calculator">3.14 * 2.25</gadget>
<output>7.065</output>

<gadget id="calculator">28.26 - 7.065</gadget>
<output>21.195</output>

<result>21.195</result>