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: a shopkeeper sells his goods at cost price but uses a faulty meter that weighs 800 grams . find the profit percent . 
Options: a ) 20 , b ) 15 , c ) 25 , d ) 18 , e ) 19
Example Output: c

Example Input: Problem: mr . karan borrowed a certain amount at 6 % per annum simple interest for 9 years . after 9 years , he returned rs . 8310 / - . find out the amount that he borrowed . 
Options: a ) s . 5266 , b ) s . 5396 , c ) s . 5228 , d ) s . 5218 , e ) s . 52192
Example Output: b

Example Input: Problem: a chemist mixes one liter of pure water with x liters of a 50 % salt solution , and the resulting mixture is a 15 % salt solution . what is the value of x ? 
Options: a ) 1 / 4 , b ) 1 / 3 , c ) 1 / 2 , d ) 1 , e ) 3 / 7
Example Output:
e