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 hiker walked for 3 days. she walked 18 miles on the first day, walking 3 miles per hour. on the second day she walked for one less hour but she walked one mile per hour, faster than on the first day. on the third day 5 miles per hour for 6 hours. how many miles in total did she walk ?
Options: a. 68, b. 44, c. 58, d. 60, e. 62
[EX A]: a

[EX Q]: Problem: buses a and b start from a common bus stop x. bus a begins to travel in a straight line away from bus b at a constant rate of 20 miles per hour. one hour later, bus b begins to travel in a straight line in the exact opposite direction at a constant rate of 80 miles per hour. if both buses travel indefinitely, what is the positive difference, in minutes, between the amount of time it takes bus b to cover the exact distance that bus a has covered and the amount of time it takes bus b to cover twice the distance that bus a has covered ?
Options: a. 36, b. 72, c. 132, d. 144, e. 180
[EX A]: c

[EX Q]: Problem: what is the x - intercept of a line that passes through the point ( 3, 4 ) and has a slope of 2 ?
Options: a. - 2, b. - 1, c. 0, d. 1, e. 2
[EX A]:
d