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: 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: if the perimeter of a rectangular garden is 700 m, its length when its breadth is 100 m is ?
Options: a. 299 m, b. 777 m, c. 200 m, d. 250 m, e. 128 m

Ex Output:
d

Ex Input:
Problem: what is the value of 3 x ^ 2 1.8 x + 0.3 for x = 0.9 ?
Options: a. 0.3, b. 0, c. 0.3, d. 1.11, e. 2.46

Ex Output:
d