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: a copy machine, working at a constant rate, makes 35 copies per minute. a second copy machine, working at a constant rate, makes 65 copies per minute. working together at their respective rates, how many copies do the two machines make in half an hour ?
Options: a. 3,000, b. 2,700, c. 4,500, d. 5,400, e. 324,000
[EX A]: a

[EX Q]: Problem: what is the value of ( 2 ) ^ - 3 ?
Options: a. 1 / 6, b. 1 / 5, c. 1 / 8, d. 1 / 9, e. 1 / 7
[EX A]: c

[EX Q]: Problem: the speed of a boat in still water is 14 km / hr and the rate of current is 5 km / hr. the distance travelled downstream in 8 minutes is
Options: a. 1.6 km, b. 2.5 km, c. 3.6 km, d. 4 km, e. none of these
[EX A]:
b