A water pipe is circular in cross section, with an inner diameter of 8 cm and an outer diameter of 10 cm. What is the cross-sectional area of the iron pipe in square centimeters?
一种水管横截面为环形，内直径8厘米，外直径10厘米，铁管的横截面面积是多少平方厘米？
<gadget id="calculator">10 / 2</gadget>
<output>5</output>

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

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

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

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

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<result>28.26</result>