The outer diameter of a ring-shaped iron piece is 12cm, the inner diameter is 8cm, what is the area of the ring-shaped iron piece in cm**2.
一个环形的铁片的外直径是12cm，内直径是8cm，环形铁片的面积是多少cm**2．
<gadget id="calculator">12 / 2</gadget>
<output>6</output>

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

<gadget id="calculator">8 / 2</gadget>
<output>4</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>