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.

[EX Q]: Problem: a certain library assesses fines for overdue books as follows. on the first day that a book is overdue, the total fine is $ 0.09. for each additional day that the book is overdue, the total fine is either increased by $ 0.30 or doubled, whichever results in the lesser amount. what is the total for a book on the fourth day it is overdue ?
Options: a. $ 0.66, b. $ 0.70, c. $ 0.80, d. $ 0.90, e. $ 1.00
[EX A]: a

[EX Q]: Problem: how many prime numbers are between 29 / 3 and 87 / 6 ?
Options: a. 1, b. 2, c. 3, d. 4, e. 5
[EX A]: b

[EX Q]: Problem: a man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. the ratio of the speed of the boat ( in still water ) and the stream is
Options: a. 1: 2, b. 1: 3, c. 2: 1, d. 3: 1, e. none
[EX A]:
d