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: the mean proportional between 4 and 16 is ?
Options: a. 12, b. 13, c. 14, d. 15, e. 16
[EX A]: e

[EX Q]: Problem: last year elaine spent 20 % of her annual earnings on rent. this year she earned 20 % more than last year and she spent 30 % of her annual earnings on rent. the amount she spent on rent this year is what percent of the amount spent on rent last year ?
Options: a. 185.5, b. 180.0, c. 167.5, d. 172.5, e. 177.5
[EX A]: b

[EX Q]: Problem: find the value of ( 100 + 20 / 90 ) × 90
Options: a. 4520, b. 9100, c. 9150, d. 8120, e. 9020
[EX A]:
e