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.
Q: Problem: a total of $ 20,000 was invested in two certificates of deposit at simple annual interest rates of 6 percent and 12 percent, respectively. if the total interest on the two certificates was $ 1,440 at the end of one year, what fractional part of the $ 20.000 was invested at the higher rate ?
Options: a. 3 / 8, b. 2 / 5, c. 1 / 5, d. 3 / 5, e. 3 / 4
A:
c