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

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

S1 = v1 * t1 – the path to the pier.
S2 = v2 * t2 – return path.
S1 = S2.
v1 * t1 = v2 * t2.
v1 = 18 + 2 = 20 km / h.
v2 = 18 – 2 = 16 km / h.
t1 + t2 = 4.5 hours.
t1 = 4.5 – t2.
20 * (4.5 – t2) = 16 * t2.
t2 = 2.5.
S2 = 16 * 2.5.
S2 = 40.
Answer: Between the quays 40 km.