Make 10 cylindrical ventilation pipes with iron sheets, each section is 9 decimeters long, and the bottom circumference is 3.5 decimeters. How many square meters of iron sheets are needed at least?
用铁皮制作圆柱形的通风管10节，每节长9分米，底面周长3.5分米，至少需要铁皮多少平方米？
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">3.5 * 9 * (1/10)</gadget>
<output>3.15</output>

<result>3.15</result>