What is the surface area of a ventilation pipe with a length of 5 meters and a diameter of 2 decimeters at the bottom?
一根长5米，底面直径2分米的通风管，表面积是多少平方分米．
<gadget id="calculator">5 * 10</gadget>
<output>50</output>

<gadget id="calculator">3.14 * 2 * 50</gadget>
<output>314</output>

<result>314</result>