A ring has an inner diameter of 6 cm and a width of 2 cm. What is the area of the ring?
一个圆环，内直径是6厘米，环宽2厘米，圆环的面积是多少．
<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>