The silver part of the disc is a ring, the diameter of the inner circle is 6cm, and the width of the ring is 2cm. What is the area of the silver part?
光盘的银色部分是一个圆环，内圆直径是6cm，环宽是2cm．银色部分的面积是多少．
<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">25 - 9</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<result>50.24</result>