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: 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 A]: b

[EX Q]: Problem: mr. loyd wants to fence his square shaped land of 120 sqft each side. if a pole is laid every 12 ft how many poles do he need ?
Options: a. 20, b. 30, c. 40, d. 50, e. 60
[EX A]: c

[EX Q]: Problem: it takes avery 3 hours to build a brick wall while tom can do it in 4 hours. if the two start working together and after an hour avery leaves, how much time will it take tom to complete the wall on his own ?
Options: a. 25 minutes., b. 55 minutes., c. 1 hour and 41 minutes, d. 1 hour and 35 minutes, e. 1 hour and 20 minutes
[EX A]:
c