Instructions: 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.
Input: Problem: sara bought both german chocolate and swiss chocolate for some cakes she was baking. the swiss chocolate cost $ 2.5 per pound, and german chocolate cost $ 1.5 per pound. if the total the she spent on chocolate was $ 30 and both types of chocolate were purchased in whole number of pounds, how many total pounds of chocolate she purchased ?
Options: a. 7, b. 18, c. 10, d. 12, e. 11
Output:
b