The radius of the outer circle of a ring is 6 cm, and the radius of the inner circle is 3 cm, what is the area in cm**2.
一圆环的外圆半径6厘米，内圆半径3厘米，面积多少cm**2．
<gadget id="calculator">6 ** 2</gadget>
<output>36</output>

<gadget id="calculator">3.14 * 36</gadget>
<output>113.04</output>

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

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

<gadget id="calculator">113.04 - 28.26</gadget>
<output>84.78</output>

<result>84.78</result>