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

### Instruction:
 图书馆有9,900本书。在夏天期间，他们卖掉了一些书。如果只剩下四分之六的书，他们卖掉了多少本？


### Response:
 卖掉的书的数量是9,900 - (4/6 * 9,900) = <<9900-(4/6*9900)=3300>>3300本。