An woman sitting in a train which is travelling at 25 kmph observes that a goods train travelling in a opposite direction, takes 3 seconds to pass him. If the goods train is 140 m long, find its speed. Choices.
A) 141  B) 142  C) 143  D) 144  E) 145

Rationale: "relative speed = ( 140 / 3 ) m / s = ( 140 / 3 ) * ( 18 / 5 ) = 168 kmph speed of goods train = 168 - 25 = 143 kmph answer is c"
Answer: C