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 retailer bought a machine at a wholesale price of $ 90 and later on sold it after a 10 % discount of the retail price . if the retailer made a profit equivalent to 20 % of the whole price , what is the retail price t of the machine ? 
Options: a ) 81 , b ) 100 , c ) 120 , d ) 135 , e ) 160
Example Output: c

Example Input: Problem: what will be the difference between simple and compound interest @ 20 % per annum on a sum of $ 500 after 2 years ? 
Options: a ) $ 10 , b ) $ 20 , c ) $ 25 , d ) $ 30 , e ) $ 40
Example Output: b

Example Input: Problem: a certain maroon paint contains 50 percent blue pigment and 50 percent red pigment by weight . a certain green paint contains 30 percent blue pigment and 70 percent yellow pigment . when these paints are mixed to produce a brown paint , the brown paint contains 40 percent blue pigment . if the brown paint weighs 10 grams , then the red pigment contributes how many grams of that weight ? 
Options: a ) 3 , b ) 3.5 , c ) 2.5 , d ) 4 , e ) 4.5
Example Output:
c