The speed of the river is 5 m / s, its width is 32 m. Crossing the river in a boat, the speed of which relative to the water

The speed of the river is 5 m / s, its width is 32 m. Crossing the river in a boat, the speed of which relative to the water is 4 m / s, the helmsman provided the least possible drift of the boat by the current. What is this demolition.

Vp = 5 m / s
Vo = 4 m / s
S-?
Vl- relative to the coast Vl = Vр + Vo (vector)
since Vр = 5 Vо = 4 form a triangle, then Vл = 3 (relative to the coast)
find the angle between the vector Vl and Vp
cosa = Vl / Vr = 3/5 = 0.6
sina = √1-cos ^ 2a = √1-0.36 = 0.8
We find Vу = Vl * sina = 3 * 0.8 = 2.4 m / s
t = H / Vy = 32 / 2.4 = 13.33 s
S = Vx * t = Vl * cosa * t = 3 * 0.6 * 32 / 2.4 = 24 m