Give the step-by-step reasoning process and then the final answer. Rebecca drinks half a bottle of soda a day. She bought three 6-packs of sodas the last time she was at the store. How many bottles of soda will she have left after four weeks?

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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Rebecca bought 3 * 6 = 18 bottles of soda. A week is 7 days, so she will drink 4 * 7 = 28 half bottles of soda in four weeks. A bottle is two half bottles, so she will drink 28 / 2 = 14 bottles of soda in four weeks. Thus, after 4 weeks, she will have 18 - 14 = 4 bottles of soda left.
The final answer: 4.