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: 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: 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
c

Problem: the moon revolves around the earth at a speed of approximately 0.2 kilometers per second. this approximate speed is how many kilometers per hour ?
Options: a. 60, b. 720, c. 62.5, d. 3,600, e. 3,672
b