Q: 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.
Problem: a feed store sells two varieties of birdseed: brand a, which is 40 % millet and 60 % sunflower, and brand b, which is 65 % millet and 35 % safflower. if a customer purchases a mix of the two types of birdseed that is 50 % millet, what percent of the mix is brand b ?
Options: a. 40 %, b. 45 %, c. 50 %, d. 60 %, e. 55 %
A:
a