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: the cost of 8 dozen pencil and 2 dozen note book is 520 rupee. if cost of 3 pencil and 4 note book is 60 rupee, then sum of the cost of 1 pencil and 1 note book will be ( in rupee.
Options: a. rs 13.51, b. rs 15.51, c. rs 16.51, d. rs 14.51, e. rs 17.51
[EX A]: b

[EX Q]: Problem: two cyclist start from the same places in opposite directions. one is going towards north at 30 kmph and the other is going towards south 40 kmph. what time will they take to be 50 km apart ?
Options: a. 1.32 hr, b. 0.714 hrs, c. 3.231 hrs, d. 0.515 hrs, e. 6.214 hrs
[EX A]:
b