The outer diameter of a ring is 8 cm and the inner diameter is 6 cm. What is the area of the ring in square centimeters?
一个圆环的外圆直径是8cm，内圆直径是6cm，这个圆环的面积是多少平方厘米？
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

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

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

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

<gadget id="calculator">16 - 9</gadget>
<output>7</output>

<gadget id="calculator">3.14 * 7</gadget>
<output>21.98</output>

<result>21.98</result>