Make a cylindrical ventilation pipe with a circumference of 18.84 decimeters and a length of 4 decimeters. At least how many square decimeters of iron sheet are needed.
做一节圆柱形的通风管，底面周长18.84分米，长4分米．至少需要铁皮多少平方分米．
<gadget id="calculator">18.84 * 4</gadget>
<output>75.36</output>

<result>75.36</result>