A boat went upstream and lost a wooden stick on the way. It was only found after 2 minutes, and it was chased immediately. Q: How long does it take to catch up? The speed of the boat in still water is 18 km/h.
一艘船逆流而上，途中丢失了一根木棍，2分钟后才发现，立刻去追．问：多久才能追上？已知船的静水速度为18千米/小时．
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