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.

Example Input: Problem: the present worth of rs. 2310 due years hence, the rate of interest being 15 % per annum, is :
Options: a. rs. 1440, b. rs. 1750, c. rs. 1680, d. rs. 1840, e. none of these
Example Output: c

Example Input: Problem: the batting average of a particular batsman is 60 runs in 46 innings. if the difference in his highest and lowest score is 140 runs and his average excluding these two innings is 58 runs, find his highest score.
Options: a. 179, b. 367, c. 269, d. 177, e. 174
Example Output: e

Example Input: Problem: two pipes a and b separately fill in 15 / 2 min and 5 min respactively and third pipe c can empty of 14 l / m if all the pipes are open when the cistern is full, it is emptied in 1 hr. how many litres does the cistern hold ?
Options: a. 40, b. 30, c. 50, d. 80, e. 54
Example Output:
a