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

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

<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">1 ** 2</gadget>
<output>1</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">3.14 * 3</gadget>
<output>9.42</output>

<result>9.42</result>