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: find the simple interest on rs . 520 for 7 months at 8 paisa per month ? 
Options: a ) 277 , b ) 270 , c ) 291 , d ) 266 , e ) 121
Example Output: c

Example Input: Problem: by selling 16 pens for a rupee a woman loses 5 % . how many for a rupee should he sell in order to gain 18 % ? 
Options: a ) 12 , b ) 14 , c ) 45 , d ) 13 , e ) 65
Example Output: d

Example Input: Problem: the difference between the compound interest compounded annually and simple interest for 2 years at 20 % per annum is rs . 216 . find the principal ? 
Options: a ) 2277 , b ) 2667 , c ) 5400 , d ) 2766 , e ) 1811
Example Output:
c