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: two trains, one from howrah to patna and the other from patna to howrah, start simultaneously. after they meet, the trains reach their destinations after 10 hours and 8 hours respectively. the ratio of their speeds is
Options: a. 4: 9, b. 4: 3, c. 4: 12, d. 4: 8, e. 4: 5
[EX A]: e

[EX Q]: Problem: find the maximum value of the function f ( x ) = x − 5 if x is a number between - 5 and 13.
Options: a. 6, b. 7, c. 8, d. 9, e. none
[EX A]: c

[EX Q]: Problem: a small pool filled only with water will require an additional 300 gallons of water in order to be filled to 80 % of its capacity. if pumping in these additional 300 gallons of water will increase the amount of water in the pool by 25 %, what is the total capacity of the pool in gallons ?
Options: a. 1875, b. 1250, c. 1300, d. 1600, e. 1625
[EX A]:
a