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 person buys an article at $ 600. at what price should he sell the article so as to make a profit of 8 % ?
Options: a. 670, b. 689, c. 648, d. 740, e. 889
[A]: c


[Q]: Problem: if the price of a certain computer increased 30 percent from b dollars to 351 dollars, then 2 b =
Options: a. 540, b. 570, c. 619, d. 649, e. 700
[A]: a


[Q]: Problem: if a ^ 2 + b ^ 2 = 15 and ab = 25, what is the value of the expression ( a - b. ^ 2 + ( a + b. ^ 2 ?
Options: a. 10, b. 20, c. 30, d. 60, e. 50
[A]:
e