How long does a train 250 meters long running at the rate of 72km/hr take to cross a bridge 150 meters in length?  Choose the correct choice from the following options:
A) 10 sec
B) 20 sec
C) 25 sec
D) 30 sec
E) 35 sec

Rationale: "distance = length of train + length of bridge = 250 + 150 = 400 speed = 72 km / hr = 72 * 5 / 18 = 20 m / s required time = 400 / 20 = 20 seconds answer is b"
Answer: B