In this task, you need to answer the given multiple-choice question on the gain. Gain is the value by which to multiply the input. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: the salary of a person was reduced by 10 % . by what percent should his reduced salary be raised so as to bring it at par with his original salary ? 
Options: a ) 10 % , b ) 11 1 / 9 % , c ) 13 2 / 7 % , d ) 15 3 / 11 % , e ) 12 1 / 3 %
Example Output: b

Example Input: Problem: a family made a down payment of $ 300 and borrowed the balance on a set of encyclopedias that cost $ 750 . the balance with interest was paid in 9 monthly payments of $ 57 each and a final payment of $ 21 . the amount of interest paid was what percent of the amount borrowed ? 
Options: a ) 6 % , b ) 12 % , c ) 14 % , d ) 18.66 % , e ) 20 %
Example Output: d

Example Input: Problem: calculate how long it will take a swimmer to swim a distance of 7 km against the current of a river which flows at 2.5 km / hr , given that he can swim in still water at 4.4 km / h 
Options: a ) 6.67 , b ) 1.67 , c ) 2.67 , d ) 3.67 , e ) 4.67
Example Output:
d