Teacher: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'.
Teacher: Now, understand the problem? Solve this instance: Problem: a train covers a distance of 18 km in 3 min . if it takes 4 sec to pass a telegraph post , then the length of the train is ? 
Options: a ) 370 , b ) 380 , c ) 390 , d ) 400 , e ) 410
Student:
d