The ship moves along the lake from west to east at a speed of 72 km / h. when the north wind blew

The ship moves along the lake from west to east at a speed of 72 km / h. when the north wind blew, the speed measured on the ship turned out to be 25 m / s. what is the actual wind speed.

Let’s link the frame of reference to the ship.
The wind speed caused by the movement of the ship will be Vк = 72 km / h = 72000 m / 3600 s = 20 m / s and will be directed from east to west.
The actual wind speed Vb relative to the lake (and relative to the ship) will be directed from north to south.
The measured velocity Vi will be equal to the vector sum of the velocities Vc and Vv perpendicular to each other. The vector sum of the velocities will be numerically equal to the diagonal of the rectangle built on the velocity vectors.
Vi² = Vк² + Vв²;
Vв = √ (Vi² – Vк²) = √ ((25 m / s) ² – (20 m / s) ²) = 15 m / s.
Answer: 15 m / s.