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: a and b together can complete work in 6 days. a alone starts working and leaves it after working for 4 days completing only half of the work. in how many days it can be completed if the remaining job is undertaken by b ?
Options: a. 4, b. 12, c. 5, d. 6, e. 7
[EX A]: b

[EX Q]: Problem: what is the area of a regular hexagon with sides 1 in. long ?
Options: a. 1.59 square inch, b. 2.59 square inch, c. 3.59 square inch, d. 4.59 square inch, e. 2.69 square inch
[EX A]: b

[EX Q]: Problem: a train is running at a speed of 40 km / hr and it crosses a post in 22.5 seconds. what is the length of the train ?
Options: a. 190 metres, b. 160 metres, c. 200 metres, d. 120 metres, e. 250 metres
[EX A]:
e