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: if the average ( arithmetic mean ) of a and b is 45 and the average of b and c is 80, what is the value of c − a ?
Options: a. 25, b. 60, c. 90, d. 140, e. it can not be determined from the information given.
[EX A]: b

[EX Q]: Problem: what is the units digit of 32 ! + 50 ! + 4 ! + 4 ! ?
Options: a. 0, b. 2, c. 4, d. 6, e. 8
[EX A]: e

[EX Q]: Problem: the sum of ages of 5 children born at the intervals of 3 years each is 55 years. what is the age of the youngest child ?
Options: a. 5 years, b. 4 years, c. 6 years, d. 7 years, e. 8 years
[EX A]:
a