You will be given a definition of a task first, then some input of the task.
In this task, you need to answer the given multiple-choice question on the physics. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Problem: a train 850 m long is running at a speed of 78 km / hr . if it crosses a tunnel in 1 min , then the length of the tunnel is ? 
Options: a ) 510 , b ) 450 , c ) 500 , d ) 520 , e ) 589
Output:
b