What is the surface area of a circular tube with a length of 6 meters and a cross-sectional circumference of 3.14 meters?
一根长6米圆管，截面周长为3.14米，其表面积为多少．
<gadget id="calculator">3.14 * 6</gadget>
<output>18.84</output>

<gadget id="calculator">3.14 / 3.14 / 2</gadget>
<output>0.5</output>

<gadget id="calculator">0.5 ** 2</gadget>
<output>0.25</output>

<gadget id="calculator">3.14 * 0.25</gadget>
<output>0.785</output>

<gadget id="calculator">0.785 * 2</gadget>
<output>1.57</output>

<gadget id="calculator">18.84 + 1.57</gadget>
<output>20.41</output>

<result>20.41</result>