How much time will a train of length 280 m moving at a speed of 72 kmph take to cross another train of length 360 m, moving at 36 kmph in the same direction?  Choose the correct option:
A) 50
B) 99
C) 64
D) 76
E) 12

Rationale: "the distance to be covered = sum of their lengths = 280 + 360 = 640 m . relative speed = 72 - 36 = 36 kmph = 36 * 5 / 18 = 10 mps . time required = d / s = 640 / 10 = 64 sec . answer : c"
Answer: C