The outer diameter of a ring is 36 cm and the ring width is 6 cm. What is the area of the ring?
一个圆环的外直径是36厘米，环宽6厘米，这个环形的面积是多少．
<gadget id="calculator">36 / 2</gadget>
<output>18</output>

<gadget id="calculator">18 ** 2</gadget>
<output>324</output>

<gadget id="calculator">3.14 * 324</gadget>
<output>1_017.36</output>

<gadget id="calculator">18 - 6</gadget>
<output>12</output>

<gadget id="calculator">12 ** 2</gadget>
<output>144</output>

<gadget id="calculator">3.14 * 144</gadget>
<output>452.16</output>

<gadget id="calculator">1_017.36 - 452.16</gadget>
<output>565.2</output>

<result>565.2</result>