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: in what time will a train 50 m long cross an electric pole, it its speed be 360 km / hr ?
Options: a. 0.25, b. 0.5, c. 1.5, d. 2.5, e. 3.5
[EX A]: b

[EX Q]: Problem: a 24 ' ' x 24 ' ' square metal plate needs to be fixed by a carpenter on to a wooden board. the carpenter uses nails all along the edges of the square such that there are 25 nails on each side of the square. each nail is at the same distance from the neighboring nails. how many nails does the carpenter use ?
Options: ['a. 94', 'b. 95', 'c. 96', 'd. 97', 'e. 98']
[EX A]: c

[EX Q]: Problem: the total age of a and b is 16 years more than the total age of b and c. c is how many year younger than
Options: a. 14 years, b. 12 years, c. 56 years, d. 16 years, e. 55 years
[EX A]:
d