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.

Problem: if the sides of a cube are in the ratio 5: 3. what is the ratio of their diagonals ?
Options: ['a. 5: 9', 'b. 9: 3', 'c. 5: 4', 'd. 3: 5', 'e. 5: 3']
e

Problem: to deliver an order on time, a company has to make 25 parts a day. after making 25 parts per day for 3 days, the company started to produce 5 more parts per day, and by the last day of work 100 more parts than planned were produced. find how many parts the company made and how many days this took.
Options: a. 600, b. 500, c. 575, d. 655, e. 675
e

Problem: the average age of 15 students of a class is 15 years. out of these, the average age of 6 students is 14 years and that of the other 8 students is 16 years. the age of the 15 th student is
Options: a. 9 years, b. 13 years, c. 14 years, d. 21 years, e. 25 years

b