A ring has an outer radius of 5 decimeters and an inner radius of 3 decimeters. What is the area of the ring in square decimeters?
一个圆环，外圆半径5分米，内圆半径3分米，这个圆环的面积是多少平方分米？
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

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

<gadget id="calculator">25 - 9</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<result>50.24</result>