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 Input:
Problem: set s consists of integers { 7, 8, 10, 12, 13 }. if integer n is included in the set, the average ( arithmetic mean ) of set s will increase by 10 %. what is the value of integer n ?
Options: a. 10, b. 12, c. 16, d. 22, e. 24

Ex Output:
c


Ex Input:
Problem: 210 students were asked in a survey if they preferred windows or mac brand computers. 60 students claimed that they preferred mac to windows brand computers. one third as many of the students who preferred mac to windows, equally preferred both brands. 90 of the students had no preference. how many of the students in the survey preferred windows to mac brand computers ?
Options: a. 25, b. 40, c. 50, d. 60, e. 75

Ex Output:
b


Ex Input:
Problem: in the x - y plane, there are 4 points ( 0,0 ), ( 0,4 ), ( 8,4 ), and ( 8,0 ). if these 4 points makes a rectangle, what is the probability that x + y < 4 ?
Options: a. 1 / 2, b. 1 / 3, c. 2 / 3, d. 1 / 4, e. 2 / 5

Ex Output:

d