A 300 m long train crosses a platform in 39 sec while it crosses a signal pole in 24 sec. What is the length of the platform?  Pick
A) 389 m B) 350 m C) 187.5 m D) 299 m E) 219.5 m

Rationale: "speed = 300 / 24 = 25 / 2 m / sec . let the length of the platform be x meters . then , ( x + 300 ) / 39 = 25 / 2 = > x = 187.5 m . answer : c"
Answer: C