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 70 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. 15, b. 20, c. 40, d. 42, e. 68
d

Problem: if a and b are positive real numbers, and a ^ 3 + b ^ 3 = 25, then the greatest possible value of a is between :
Options: a. 0 and 3, b. 3 and 4, c. 4 and 5, d. 5 and 7, e. 7 and 9
a

Problem: a reduction of 22 % in the price of salt enables a lady to obtain 10 kgs more for rs. 100, find the original price per kg ?
Options: a. s. 2.82, b. s. 2.4, c. s. 2.5, d. s. 2.2, e. s. 2.1
a