The boat’s own speed is 8.5 km / h, the speed of the river is 1.5 km / h. The distance between the marinas is 17.5 km.

The boat’s own speed is 8.5 km / h, the speed of the river is 1.5 km / h. The distance between the marinas is 17.5 km. How long will the boat take this distance if it is sailing against the stream of the river?

Let’s find the speed of the boat against the current, (the speed will be less than the boat’s own speed, since the current will slow down the boat):
8.5 – 1.5 = 7 km / h;
Let’s find the time it takes for the boat to travel the path between the piers:
t = S: V = 17.5: 7 = 2.5 h.
Answer: 2.5 hours