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 median of a set of consecutive integers if the sum of nth number from the beginning and nth number from the end is 110 ?
Options: a. 10, b. 25, c. 55, d. 75, e. 100
[EX A]: c

[EX Q]: Problem: you collect baseball cards. suppose you start out with 15. maria takes half of one more than the number of baseball cards you have. since you ' re nice, you give peter 1 baseball card. since his father makes baseball cards, paul decides to triple your baseball cards. how many baseball cards do you have at the end ?
Options: a. 17, b. 18, c. 19, d. 20, e. 21
[EX A]:
b