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.

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
b

Problem: excluding stoppages, the average speed of a bus is 60 km / hr and including stoppages, the average speed of the bus is 40 km / hr. for how many minutes does the bus stop per hour ?
Options: a. 18 min, b. 17 min, c. 19 min, d. 20 min, e. 21 min
d

Problem: difference of 2 numbers is 100. if 5 % of one number is 10 % of the other number, find the addition of 2 numbers ?
Options: a. 150, b. 300, c. 210, d. 290, e. 180

b