A 300 m long train crosses a platform in 45 sec while it crosses a signal pole in 18 sec. What is the length of the platform?  Select the correct option:  A) 287  B) 350  C) 828  D) 450  E) 122

Rationale: "speed = 300 / 18 = 50 / 3 m / sec . let the length of the platform be x meters . then , ( x + 300 ) / 45 = 50 / 3 3 x + 900 = 2250 = > x = 450 m . answer : d"
Answer: D