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: a man sitting in a train which is travelling at 64 kmph observes that a goods train travelling in a opposite direction , takes 18 seconds to pass him . if the goods train is 420 m long , find its speed . 
Options: a ) 32 , b ) 15 , c ) 18 , d ) 20 , e ) 25
Example Output: d

Example Input: Problem: twelve machines , each working at the same constant rate , together can complete a certain job in 6 days . how many additional machines , each working at the same constant rate , will be needed to complete the job in 3 days ? 
Options: a ) 14 , b ) 12 , c ) 15 , d ) 16 , e ) 18
Example Output: b

Example Input: Problem: a train leaves mumabai at 9 am at a speed of 40 kmph . after one hour , another train leaves mumbai in the same direction as that of the first train at a speed of 50 kmph . when and at what distance from mumbai do the two trains meet ? 
Options: a ) 276 , b ) 271 , c ) 200 , d ) 278 , e ) 268
Example Output:
c