The boat covered the distance between the quays there and back in 4.5 hours. The speed of the river flow was 2 km / h.

The boat covered the distance between the quays there and back in 4.5 hours. The speed of the river flow was 2 km / h. The boat’s own speed is 18 km / h. Find the distance between the marinas.

If the boat’s own speed is 18 km / h, then the downstream speed is 18 + 2 = 20 km / h, upstream – 18-2 = 16 km / h. Let’s take the distance between the piers as x. It follows from the condition of the problem that the boat spent 4.5 hours on the way there (x / 20) and back (x / 16). Let’s make an equation. x / 20 + x / 16 = 4.5. Let’s bring to a common denominator – 80. We get 4x + 5x = 360. 9x = 360.
x = 40 km.
Answer: the distance between the marinas is 40 km.