cylinder is surrounded by a piece of rectangular paper with a length of 13dm and a width of 7dm. What is its lateral area?
用一张长13dm，宽7dm的长方形纸围成一个圆柱，它的侧面积是多少．
<gadget id="calculator">13 * 7</gadget>
<output>91</output>

<result>91</result>