A ring has an inner radius of 4 cm and an outer radius of 6 cm. What is the area of the ring in cm**2.
一个圆环，内圆半径是4cm，外圆半径是6cm，这个圆环的面积是多少cm**2．
<gadget id="calculator">6 ** 2</gadget>
<output>36</output>

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

<gadget id="calculator">36 - 16</gadget>
<output>20</output>

<gadget id="calculator">3.14 * 20</gadget>
<output>62.8</output>

<result>62.8</result>