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: 150 is what percent of 60 ? 
Options: a ) 250 % , b ) 20 % , c ) 50 % , d ) 200 % , e ) 500 %
Example Output: a

Example Input: Problem: a sum of money at simple interest amounts to $ 815 in 3 years and to $ 854 in 4 years . the sum is : 
Options: a ) $ 153 , b ) $ 698 , c ) $ 398 , d ) $ 549 , e ) $ 675
Example Output: b

Example Input: Problem: two men started from the same place walk at the rate of 5 kmph and 5.5 kmph respectively . what time will they take to be 8.5 km apart , if they walk in the same direction ? 
Options: a ) 10 hours , b ) 12 hours , c ) 17 hours , d ) 15 hours , e ) 20 hours
Example Output:
c