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: what is the rate percent when the simple interest on rs. 810 amount to rs. 155 in 4 years ?
Options: a. 4.78, b. 4.68, c. 4.58, d. 4.48, e. 4.38
Example Output: a

Example Input: Problem: four bells commence tolling together and toll at intervals of 2, 4, 6, 8 seconds respectively. in 18 minutes, how many times do they toll together ?
Options: a. 43, b. 44, c. 45, d. 46, e. 47
Example Output: c

Example Input: Problem: a sum of money is distributed among a, b, c, d in the proportion of 5: 2: 4: 3. if c gets $ 1000 more than d, what is the b ' s share ?
Options: a. $ 1000, b. $ 2000, c. $ 2500, d. $ 2850, e. $ 2950
Example Output:
b