Definition: Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.
Input: Problem: keats library purchases a number of new books, all in the category of biography, and the library does not acquire any other books. with the addition of the new biographies, the biography collection of the library amounts to 30 % of the total number of books in the library. if prior to the purchase, only 20 % of the books in keats library were biographies, by what percent has the number of biographies in the library increased ?
Options: a. 47 %, b. 59 %, c. 71 %, d. 83 %, e. 95 %
Output:
c