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

### Instruction:
 如果贝丝18岁，她的妹妹5岁，多少年后她的年龄会是妹妹年龄的两倍？


### Response:
 贝丝比她妹妹大18 - 5 = <<18-5=13>>13岁。
贝丝必须是13 x 2 = <<13*2=26>>26岁才能是妹妹年龄的两倍。
贝丝将在26 - 18 = <<26-18=8>>8年后是妹妹年龄的两倍。