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: 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
[EX A]: a

[EX Q]: Problem: if ( 1 1.25 ) n = 4, then n =
Options: a. 400, b. 16, c. 4, d. 4, e. 400
[EX A]: b

[EX Q]: Problem: simple interest on a certain sum at a certain annual rate of interest is 1 / 9 of the sum. if the numbers representing rate percent and time in years be equal, then the rate of interest is :
Options: a. 5, b. 8, c. 3 1 / 3, d. 2 2 / 3, e. none of these
[EX A]:
c