A ring has an inner circle with a radius of 3 meters and an outer circle with a diameter of 8 meters. What is the area of the circle in square meters?
一个环形内圆半径3米，外圆直径8米．这个环形的面积是多少平方米？
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

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

<gadget id="calculator">16 - 9</gadget>
<output>7</output>

<gadget id="calculator">3.14 * 7</gadget>
<output>21.98</output>

<result>21.98</result>