How long will a passenger sitting at the window of a train moving at a speed of 54 km / h see an oncoming

How long will a passenger sitting at the window of a train moving at a speed of 54 km / h see an oncoming train passing by him, the speed of which is 72 km / h, if its length is 150 m?

V1 = 54 km / h = 15 m / s.
V2 = 72 km / h = 20 m / s.
L = 150 m.
t -?
Since the trains go to meet each other, the speed of the oncoming train relative to the passenger will be V = V1 + V2.
The passenger will begin to see the train when the first carriage begins to pass, and ends when the last carriage passes. A distance equal to the length of the train will pass along it with a speed V = V1 + V2.
t = L / (V1 + V2).
t = 150 m / (15 m / s + 20 m / s) = 4.29 s.
Answer: the passenger will observe the oncoming train t = 4.29 s.