Use a piece of rectangular paper with a length of 6.9 decimeters and a width of 4 decimeters to form a cylindrical paper tube. What is its side area in square decimeters?
用一张长6.9分米，宽4分米的长方形纸，围成一个圆柱形纸筒，它的侧面积是多少平方分米．
<gadget id="calculator">6.9 * 4</gadget>
<output>27.6</output>

<result>27.6</result>