Use a piece of rectangular paper with a length of 8.5 cm and a width of 5 cm to form a cylindrical paper tube. What is the lateral area of the paper tube in square centimeters?
用一张长8.5厘米，宽5厘米的长方形纸，围成一个圆柱形纸筒，这个纸筒的侧面积是多少平方厘米．
<gadget id="calculator">8.5 * 5</gadget>
<output>42.5</output>

<result>42.5</result>