A circular iron ring has an inner radius of 5 cm and an outer radius of 7 cm, what is the area of its annular part in cm**2.
一个环形铁环，内圆半径为5厘米，外圆半径是7厘米，它的环形部分的面积为多少cm**2．
<gadget id="calculator">7 ** 2</gadget>
<output>49</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">49 - 25</gadget>
<output>24</output>

<gadget id="calculator">3.14 * 24</gadget>
<output>75.36</output>

<result>75.36</result>