circle has an outer radius of 5 cm and an inner radius of 3 cm, what is the area of the ring in square centimetres?
一个环形外圆半径5厘米，内圆半径3厘米，圆环面积是多少平方厘米．
<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>