Two bullet train s 140 m and 210 m long run at the speed of 60 km/hr and 40 km/hr respectively in opposite directions on parallel tracks. The time (in seconds) which they take to cross each other, is:	Choose the correct option:
A) 15.8 sec .
B) 12.6 sec .
C) 11.8 sec .
D) 10.8 sec .
E) 08.8 sec .

Rationale: "relative speed = ( 60 + 40 ) km / hr = 100 x 5 / 18 = 250 / 9 m / sec . distance covered in crossing each other = ( 140 + 210 ) m = 350 m . required time = 350 x 9 / 250 = 54 / 5 = 12.6 sec . answer b"
Answer: B