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: 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
c

Problem: car x began traveling at an average speed of 35 miles per hour. after 72 minutes, car y began traveling at an average speed of 49 miles per hour. when both cars had traveled the same distance, both cars stopped. how many miles did car x travel from the time car y began traveling until both cars stopped ?
Options: a. 105, b. 120, c. 140, d. 147, e. 168
a

Problem: at a certain bowling alley, it costs $ 0.50 to rent bowling shoes for the day and $ 1.25 to bowl 2 games. if a person has $ 12.80 and must rent shoes, what is the greatest number of complete games that person can bowl in one day ?
Options: a. 7, b. 8, c. 9, d. 19, e. 21

d