A 300 m long train crosses a platform in 39 sec while it crosses a signal pole in 10 sec. What is the length of the platform? Choose the correct choice from the following choices.
A) 187 m  B) 350 m  C) 267 m  D) 287 m  E) 870 m

Rationale: "speed = 300 / 10 = 30 m / sec . let the length of the platform be x meters . then , ( x + 300 ) / 39 = 30 = > x = 870 m . answer : e"
Answer: E