A fast train with a length of l1 = 150m moves at a speed of V1 = 90km / h and overtakes a freight train

A fast train with a length of l1 = 150m moves at a speed of V1 = 90km / h and overtakes a freight train with a length of l2 = 570m moving in the same direction at a speed of V2 = 54km / h. How long will overtaking take?

l1 = 150 m.
V1 = 90 km / h = 25 m / s.
l2 = 570 m.
V2 = 54 km / h = 15 m / s.
t -?
Since trains move in one direction, the speed of a fast train relative to a freight train will be V = V1 – V2.
The fast train will start overtaking when its first point is on the same level with the last point of the freight train, and ends when the last point of the last car of the fast train aligns with the first point of the freight train.
A fast train for overtaking must pass its length l1 = 150 m and the length of a freight train l2 = 570 m at a speed V = V1 – V2.
t = (l1 + l2) / (V1 – V2).
t = (150 m + 570 m) / (25 m / s – 15 m / s) = 72 s.
Answer: overtaking a fast freight train lasts t = 72 s.