A circular steel pipe has an outer diameter of 8 cm and an inner diameter of 4 cm. What is its cross-sectional area in square centimeters?
一种圆形钢管，外直径8厘米，内直径4厘米，它的横截面面积是多少平方厘米？
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

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

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

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

<gadget id="calculator">16 - 4</gadget>
<output>12</output>

<gadget id="calculator">3.14 * 12</gadget>
<output>37.68</output>

<result>37.68</result>