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: 12. what is the dividend. divisor 17, the quotient is 9 and the remainder is 10.
Options: a. 150, b. 152, c. 154, d. 163, e. 144
[EX A]: d

[EX Q]: Problem: 18.05 ã — 0.001 = ?
Options: a. 0.1805, b. 0.01805, c. 1.805, d. 0.001805, e. none of these
[EX A]: b

[EX Q]: Problem: an empty fuel tank is filled with brand z gasoline. when the tank is 1 / 4 empty, it is filled with brand y gasoline. when the tank is half empty again, it is filled with brand z gasoline. when the tank is half empty again, it is filled with brand y gasoline. at this time, what percent of the gasoline in the tank is brand z ?
Options: a. 31.25 %, b. 30 %, c. 40 %, d. 50 %, e. 45 %
[EX A]:
a