A passenger of a train that is moving with the speed of 25 m/s sees from his seat far from a window that it takes 6 seconds for another train to pass the window completely. If the length of the second train is 300 m and it is going in the opposite direction, what is its velocity?
a) 15 m/s
b) 20 m/s
c) 25 m/s
d) 30 m/s
e) 35 m/s