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

### Instruction:
 一套7个勺子的价格是21美元。如果每个勺子单独出售，5个勺子要多少钱？


### Response:
 一套7个勺子中的一把勺子的价格是21 / 7 = 3美元。
所以5个勺子要15美元。