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 train 50 m long takes 6 sec to cross a man walking at 5 kmph in a direction opposite to that of the train . find the speed of the train ? 
Options: a ) 15 kmph , b ) 25 kmph , c ) 35 kmph , d ) 45 kmph , e ) 55 kmph
Example Output: b

Example Input: Problem: aaron will jog from home at 2 miles per hour and then walk back home by the same route at 4 miles per hour . how many miles from home can aaron jog so that he spends a total of 3 hours jogging and walking ? 
Options: a ) 5 , b ) 7 , c ) 3 , d ) 9 , e ) 10
Example Output: c

Example Input: Problem: calculate the speed of a boat in still water ( in km / hr ) if in one hour , the boat goes at 13 km / hr downstream and 4 km / hr upstream . 
Options: a ) 4.5 kmph , b ) 9.5 kmph , c ) 7.5 kmph , d ) 8.5 kmph , e ) 5.5 kmph
Example Output:
d