Two trains of length 100 meters and 200 meters are 140 meters apart. They are moving towards each other on parallel tracks, at speeds of 54 km/h and 72 km/h. After how many seconds will the trains meet? Pick one
A) 2
B) 4
C) 6
D) 8
E) 10

Rationale: "the speeds are 54000 / 3600 = 15 m / s and 72000 / 3600 = 20 m / s the relative speed is 35 m / s . time = 140 / 35 = 4 seconds the answer is b ."
Answer: B