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'.

Example Input: Problem: john traveled 80 % of the way from yellow - town to green - fields by train at an average speed of 80 miles per hour . the rest of the way john traveled by car at an average speed of v miles per hour . if the average speed for the entire trip was 60 miles per hour , what is v in miles per hour ? 
Options: a ) 30 , b ) 40 , c ) 50 , d ) 55 , e ) 70
Example Output: a

Example Input: Problem: a can finish a piece of work in 12 days . b can do it in 20 days . they work together for 9 days and then a goes away . in how many days will b finish the work ? 
Options: a ) 6 days , b ) 4 days , c ) 5 days , d ) 3 days , e ) 7 days
Example Output: c

Example Input: Problem: a train 125 m long passes a man , running at 4 km / hr in the same direction in which the train is going , in 10 seconds . the speed of the train is : 
Options: a ) 49 km / hr , b ) 50 km / hr , c ) 45 km / hr , d ) 65 km / hr , e ) 87 km / hr
Example Output:
a