The recording surface of a disc is circular, the diameter of the inner circle is 4 cm, and the diameter of the outer circle is 12 cm. What is the area of the recording surface of this disc in square centimeters?
一张光盘的刻录面为环形，内圆的直径是4厘米，外圆直径是12厘米，这张光盘刻录面的面积是多少平方厘米．
<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>2</output>

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

<gadget id="calculator">36 - 4</gadget>
<output>32</output>

<gadget id="calculator">3.14 * 32</gadget>
<output>100.48</output>

<result>100.48</result>