The cost price of an book is 64% of the marked price. Calculate the gain percent after allowing a discount of 16%?  Select the correct option: A) 31.25 % B) 35.5 % C) 37.5 % D) 39.5 % E) 30.5 %

Rationale: "let marked price = $ 100 . then , c . p . = $ 64 , s . p . = $ 84 gain % = 20 / 64 * 100 = 31.25 % . a"
Answer: A