Two trains 100 meters and 120 meters longer running in the same direction with speeds of 72 km/hr and 54 km/hr. In how much time will the first train cross the seconds?

A.  40 sec   
B.  44 sec
C.  46 sec   
D.  48 sec
Answer: B

Explanation:

Relative Speed of trains    = (72 - 54) km/hr
                                       = 18 km/hr
                                       = (18 x 5 /18) km/hr
                                       = 5 m /sec.
Time taken to cover    = (100 + 120) m/sec
                                  = (220 / 5 ) sec
                                  = 44 sec