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.
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Question: Problem: if jack walked 8 miles in 1 hour and 15 minutes, what was his rate of walking in miles per hour ?
Options: a. 4, b. 4.5, c. 6, d. 6.4, e. 15

Answer: d


Question: Problem: there are 15 balls in a jar. you take out 3 blue balls without putting them back inside, and now the probability of pulling out a blue ball is 1 / 3. how many blue balls were there in the beginning ?
Options: a. 12., b. 9., c. 8., d. 7., e. 6.

Answer: d


Question: Problem: when x is even, [ x ] = x / 2 + 1, when x is odd [ x ] = 2 x + 1 then [ 6 ] * [ 3 ] = ?
Options: a. [ 22 ], b. [ 44 ], c. [ 45 ], d. [ 28 ], e. [ 10 ]

Answer:
d