A ring has an inner diameter of 6 cm and an outer radius of 6 cm. What is the area of the ring?
一个环形，内圆直径6厘米，外圆半径是6厘米，这个环形的面积是多少．
<gadget id="calculator">6 ** 2</gadget>
<output>36</output>

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

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

<gadget id="calculator">36 - 9</gadget>
<output>27</output>

<gadget id="calculator">3.14 * 27</gadget>
<output>84.78</output>

<result>84.78</result>