A train traveling with constant speed crosses a 90m long platform in 12 seconds and a 120m long platform in 15 seconds.Find the length of the train and its speed.	Options:
A) 30 B) 40 C) 60 D) 50 E) none

Rationale: let the length of the train be x m and its speed be y m / sec . then , x / y = 12 = > y = x / 12 ( x + 90 ) / 12 = x + 120 / 15 = > x = 30 m . answer : a
Answer: A