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: an assembly line produces 15 cogs per hour until an initial order of 60 cogs is completed. the speed of the assembly line is then immediately increased so that it can produce 60 cogs per hour until another 60 cogs are produced. what is the overall average output, in cogs per hour, for the assembly line during this whole time ?
Options: a. 20, b. 22, c. 24, d. 26, e. 28

A: c
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Q: Problem: what is the total number of integers between 200 and 500 that are divisible by 25 ?
Options: a. 20, b. 25, c. 14, d. 15, e. 18

A: d
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Q: Problem: the least perfect square, which is divisible by each of 21, 36 and 66 is
Options: a. 213414, b. 213424, c. 213434, d. 213444, e. none of these

A:
d
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