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: a rope of which a calf is tied is increased from 12 m to 23 m, how much additional grassy ground shall it graze ?
Options: a. 2989, b. 2789, c. 1210, d. 1288, e. 1211
Example Output: c

Example Input: Problem: if 20 typists can type 50 letters in 30 minutes, then how many letters will 40 typists working at the same rate complete in 1 hour ?
Options: a. 400, b. 500, c. 350, d. 250, e. 200
Example Output: a

Example Input: Problem: amit and ananthu can do a work in 10 days and 20 days respectively. amit started the work and left after 2 days. ananthu took over and completed the work. in how many days was the total work completed ?
Options: a. 18 days, b. 20 days, c. 23 days, d. 25 days, e. 27 days
Example Output:
a