The silver part of a disc is a ring, the diameter of the inner circle is 4cm, and the diameter of the outer circle is 12cm, then what is the area of the silver part of the disc in cm**2.
一张光盘的银色部分是一个圆环，其内圆的直径为4cm，外圆直径为12cm，那么这张光盘银色部分的面积是多少cm**2．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">6 ** 2</gadget>
<output>36</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">36 - 16</gadget>
<output>20</output>

<gadget id="calculator">3.14 * 20</gadget>
<output>62.8</output>

<result>62.8</result>