A train 200 meters long completely crosses a 300 meters long bridge in 45 seconds. What is the speed of the train is?  Choose the correct choice from the following:
A) 10
B) 20
C) 30
D) 40
E) 50

Rationale: "s = ( 200 + 300 ) / 45 = 500 / 45 * 18 / 5 = 40 answer : d"
Answer: D