The dream cruise ship sailed 40 kilometers downstream and 16 kilometers upstream, taking 3 hours. It also took 3 hours to sail 10 kilometers downstream and 40 kilometers upstream. So, what is the sailing speed of the Dream cruise ship in still water in kilometers per hour.
梦想号游轮顺流航行40千米，再逆流航行16千米，共用3小时．而顺流航行10千米，再逆流航行40千米，也用了3小时．那么，梦想号游轮在静水中的航行速度是多少千米/小时．
<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>