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: 108 ã — 108 + 92 ã — 92 = ?
Options: a. 20120, b. 11500, c. 20128, d. 20660, e. 20228
[EX A]: c

[EX Q]: Problem: if jack walked 8 miles in 1 hour and 15 minutes, what was his rate of walking in miles per hour ?
Options: a. 4, b. 4.5, c. 6, d. 6.4, e. 15
[EX A]: d

[EX Q]: Problem: if s = x ^ 4 + y ^ 4 = 100, then the greatest possible value of x is between
Options: a. 0 and 3, b. 3 and 6, c. 6 and 9, d. 9 and 12, e. 12 and 15
[EX A]:
b