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

### Instruction:
The library has 9,900 books. Over the summer, they sold some books. If only four sixths of the books are left, how many did they sell?

### Response:
 Maktaba ilikuwa na vitabu 9,900.
Sehemu ya vitabu vilivyobaki ni 4/6.
Sehemu ya vitabu vilivyouzwa ni 2/6.
Idadi ya vitabu vilivyouzwa ni 9,900 * (2/6) = <<9900*(2/6)=3300>>3,300.