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: find the maximum value of the function f ( x ) = x − 5 if x is a number between - 5 and 13.
Options: a. 6, b. 7, c. 8, d. 9, e. none

A: c
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Q: Problem: a and b go around a circular track of length 200 m on a cycle at speeds of 36 kmph and 72 kmph. after how much time will they meet for the first time at the starting point ?
Options: a. 120 sec, b. 198 sec, c. 178 sec, d. 20 sec, e. 276 sec

A: d
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Q: Problem: if x + y = 3 and x 2 y 3 + y 2 x 3 = 27, what is the value of xy ?
Options: a. 1, b. 2, c. 3, d. 4, e. 5

A:
c
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