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

### Instruction:
 蕾贝卡每天喝半瓶苏打水。上次她在商店买了三组6瓶装的苏打水。四周后她还剩下多少瓶苏打水？


### Response:
 蕾贝卡买了3 * 6 = <<3*6=18>>18瓶苏打水。
一周有7天，所以她在四周内会喝掉28 * 1/2 = <<28*1/2=14>>14瓶苏打水。
因此，四周后她还剩下18 - 14 = <<18-14=4>>4瓶苏打水。