A steamer, moving against the current at a speed of 15 km / h, covers the distance between two

A steamer, moving against the current at a speed of 15 km / h, covers the distance between two piers in 4 hours. How long does it take to cover the same distance downstream, if its speed in this case is 5.3 m / s?

The speed of the steamer in the first case is equal to:
V1 = V – Vt = 15 km / h, V is the speed of the steamer, Vt is the speed of the current.
The speed of the steamer in the second case is:
V2 = V + Vt = 5.3 m / s = 5.3 * 3600/1000 = 19.08 km / h.
Distance is equal to:
S = V1 * t1.
S = V2 * t2.
Since the distance is the same in both cases, we equate the right-hand sides of the equations.
V1 * t1 = V2 * t2.
Hence t2 is equal to:
t2 = V1 * t1 / V2 = 15 * 4 / 19.08 ≈ 3.14 hours.

The steamer will travel downstream in 3.14 hours.