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 Input:
Problem: find the maximum value of the function f ( x ) = x − 5 if x is a number between - 5 and 13.
Options: a. 6, b. 7, c. 8, d. 9, e. none

Ex Output:
c


Ex Input:
Problem: an optometrist charges $ 150 per pair for soft contact lenses and $ 85 per pair for hard contact lenses. last week she sold 5 more pairs of soft lenses than hard lenses. if her total sales for pairs of contact lenses last week were $ 1,220, what was the total number of pairs of contact lenses that she sold ?
Options: a. 9, b. 13, c. 15, d. 17, e. 19

Ex Output:
a


Ex Input:
Problem: stacy and heather are 40 miles apart and walk towards each other along the same route. stacy walks at constant rate that is 1 mile per hour faster than heather ' s constant rate of 5 miles / hour. if heather starts her journey 24 minutes after stacy, how far from the original destination has heather walked when the two meet ?
Options: a. 4 miles, b. 8 miles, c. 17 miles, d. 6 miles, e. 12 miles

Ex Output:

c