A ring has an outer diameter of 6 decimeters and a width of 1 decimeter. What is the area of the ring?
一个圆环，外圆直径是6分米，圆环宽1分米，圆环的面积是多少．
<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

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

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

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

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<gadget id="calculator">28.26 - 12.56</gadget>
<output>15.7</output>

<result>15.7</result>