In summer, there are a lot of people swimming in Xuan'en Gongshui River. It took Xiaohua 8 minutes to swim from one escalator to the next escalator in the direction of the river flow along the river bank, and then it took him 12 minutes to return the same way. Excuse me: Xiaohua How much time does it take to walk across the two escalators while lying on the water? (Speed of downstream = speed of water + speed of people; speed of upstream = speed of people - speed of water)
夏天宣恩贡水河里面游泳的人特别多，小华沿河岸一边从一个扶梯顺着河水流动的方向游到下一扶梯用了8min，然后他又原路返回用了12min，请问：小华躺在水面上穿过两个扶梯所用的时间是多少？(顺流的速度=水流的速度+人的速度；逆流的速度=人的速度-水流的速度)
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