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

### Instruction:
 西娜正在为她姐姐的婚礼缝制伴娘的礼服。她可以在12小时内缝制一件礼服。婚礼上有5个伴娘。如果西娜每周缝制4小时，她需要多少周才能完成？


### Response:
 西娜需要60小时 / 4小时 = <<60/4=15>>15周来完成这些礼服。