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 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: at garage sale, all of the prices of the items sold were different. if the price of a radio sold at the garage sale was both the 9 th highest price and the 35 th lowest price among the prices of the items sold, how many items were sold at the garage sale ?
Options: a. 43, b. 28, c. 44, d. 49, e. 46
[A]: a


[Q]: Problem: a 70 kg metal bar made of alloy of tin and silver lost 7 kg of its weight in the water. 10 kg of tin loses 1.375 kg in the water; 5 kg of silver loses 0.375 kg. what is the ratio of tin to silver in the bar ?
Options: a. 1 / 4, b. 2 / 5, c. 1 / 2, d. 3 / 5, e. 2 / 3
[A]:
e