A 300 m long train crosses a platform in 39 sec while it crosses a signal pole in 16 sec. What is the length of the platform? Choose the correct answer: A) 287 m B) 431.25 m C) 267 m D) 287.25 m E) 656 m

Rationale: "speed = 300 / 16 = 75 / 4 m / sec . let the length of the platform be x meters . then , ( x + 300 ) / 39 = 75 / 4 = > x = 731.25 m answer : b ( 431.25 )"
Answer: B