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 average age of 15 students of a class is 15 years. out of these, the average age of 8 students is 14 years and that of the other 6 students is 16 years, the age of the 15 th student is
Options: a. 17, b. 12, c. 13, d. 14, e. 15
[EX A]: a

[EX Q]: Problem: points a, b, c, and d, in that order, lie on a line. if ab = 3 cm, ac = 4 cm, and bd = 8 cm, what is cd, in centimeters ?
Options: a. 7, b. 2, c. 3, d. 4, e. 5
[EX A]: a

[EX Q]: Problem: the average age of an adult class is 40 years. 12 new students with an avg age of 32 years join the class. therefore decreasing the average by 4 year. find what was theoriginal strength of class ?
Options: a. 8, b. 12, c. 15, d. 17, e. 18
[EX A]:
b