Make 10 cylindrical ventilation pipes, the circumference of the bottom surface is 30 cm, and the length is 1.4 m. How many square centimeters of iron sheet is needed at least?
做10节圆柱形通风管，底面周长是30厘米，长1.4米．至少需要铁皮多少平方厘米？
<result>4_200</result>