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

### Instruction:
 茉莉和她姐姐亚历克莎一起去商店买鞋。亚历克莎的鞋子是茉莉的两倍大。如果茉莉的鞋码是7，他们两个人的鞋码总和是多少？


### Response:
 如果亚历克莎的鞋子是茉莉的两倍大，那么她的鞋码是7 * 2 = <<7*2=14>>14。
两人的鞋码总和是14 + 7 = <<14+7=21>>21。