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: the area of a triangle is with base 18 m and height 6 m ?
Options: a. 88 m 2, b. 10 m 2, c. 66 m 2, d. 54 m 2, e. 31 m 2
[A]: d


[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
[A]: a


[Q]: Problem: two trains each 180 m in length are running on the same parallel lines in opposite directions with the speed of each 80 kmph. in what time will they cross each other completely ?
Options: a. 7.8 sec, b. 8.1 sec, c. 8.3 sec, d. 8.2 sec, e. 8.4 sec
[A]:
b