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: the market value of a certain machine decreased by 10 percent of its purchase price each year. if the machine was purchased in 1982 for its market value of $ 8000, what was its market value two years later ?
Options: a. $ 8,000, b. $ 5,600, c. $ 3,200, d. $ 6,400, e. $ 800
d