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: michelle deposited a certain sum of money in a savings account on july 1 st, 2007. she earns an 14 % interest compounded semiannually. the sum of money in the account on december 31 st, 2009 is approximately what percent of the initial deposit ?
Options: a. 117 %, b. 120 %, c. 121 %, d. 138 %, e. 145 %

A: d
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Q: Problem: a van takes 5 hours to cover a distance of 495 km. what speed in kph should the van maintain to cover the same distance in 3 / 2 of the previous time ?
Options: a. 60, b. 63, c. 66, d. 69, e. 72

A: c
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Q: Problem: if x, y, and z are positive real numbers such that x + y - z = 50, y - z + x = 60, and z - x + y = 80, then find the z value ?
Options: a. 10, b. 20, c. 5, d. 15, e. 25

A:
c
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