A 300 m long train crosses a platform in 30 sec while it crosses a signal pole in 18 sec. What is the length of the platform? Options:  A) 286 m  B) 350 m  C) 200 m  D) 278 m  E) 267 m

Rationale: "speed = 300 / 18 = 50 / 3 m / sec . let the length of the platform be x meters . then , ( x + 300 ) / 30 = 50 / 3 x = 200 m . answer : c"
Answer: C