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.
--------
Question: Problem: by selling 20 pencils for a rupee a man loses 30 %. how many for a rupee should he sell in order to gain 30 % ?
Options: a. 8.56, b. 10.75, c. 14.5, d. 16.5, e. 11.4

Answer: b


Question: Problem: if 20 typists can type 50 letters in 30 minutes, then how many letters will 40 typists working at the same rate complete in 1 hour ?
Options: a. 400, b. 500, c. 350, d. 250, e. 200

Answer: a


Question: Problem: a library has an average of 600 visitors on sundays and 240 on other days. the average number of visitors per day in a month of 30 days beginning with a sunday is :
Options: a. 250, b. 260, c. 300, d. 285, e. none

Answer:
c