Detailed Instructions: 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'.
Problem:Problem: the cost price of an book is 64 % of the marked price . calculate the gain percent after allowing a discount of 16 % ? 
Options: a ) 31.25 % , b ) 35.5 % , c ) 37.5 % , d ) 39.5 % , e ) 30.5 %
Solution:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
a