Below is an instruction that describes a task. Write a response that appropriately completes the request in English. Please answer in English.

### Instruction:
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?

### Response:
Rebecca bought 3 * 6 = <<3*6=18>>18 bottles of soda.
A week is 7 days, so she will drink 4 * 7 = <<4*7=28>>28 half bottles of soda in four weeks.
Since she drinks half a bottle a day, she drinks 1/2 * 28 = <<1/2*28=14>>14 bottles of soda in four weeks.
Thus, after 4 weeks, she will have 18 - 14 = <<18-14=4>>4 bottles of soda left.
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