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.

[EX Q]: Problem: what is the units digit of ( 3 ^ 13 ) ( 4 ^ 13 ) ?
Options: a. 2, b. 4, c. 6, d. 7, e. 8
[EX A]: a

[EX Q]: Problem: barbata invests $ 2200 in the national bank at 5 %. how much additional money must she invest at 8 % so that the total annual income will be equal to 6 % of her entire investment ?
Options: a. 1100, b. 3000, c. 1000, d. 3600, e. 2400
[EX A]: a

[EX Q]: Problem: twice the larger of two numbers is 3 more than 5 times the smaller, and the sum of 4 times the larger and 3 times the smaller is 71. what are the numbers ?
Options: a. 21, 12, b. 9, 0, c. 15, 6, d. 10, 1, e. 14, 5
[EX A]:
e