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 speed of a boat in still water is 15 km / hr and the rate of current is 3 km / hr. the distance travelled downstream in 24 minutes is
Options: a. 17.2 km, b. 7.2 km, c. 7.6 km, d. 17.6 km, e. 27.2 km
Example Output: b

Example Input: Problem: a 16 % stock yielding 10 % is quoted at :
Options: a. 83.33, b. 110, c. 112, d. 120, e. 160
Example Output: e

Example Input: Problem: in a group of 6 boys and 4 girls, four children are to be selected. in how many different ways can they be selected ?
Options: a. 159, b. 194, c. 210, d. 209, e. 166
Example Output:
c