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

### Instruction:
Hadley loves to do volunteer work at the local library. On a certain day, she neatly arranges 100 books on the shelf. By lunchtime, a certain number of books had been borrowed. She added 40 more books to the same shelf. By evening, 30 more books had been borrowed. If the shelf had 60 books remaining by the evening, how many books had been borrowed by lunchtime?

### Response:
 Hebu x iwe idadi ya vitabu vilivyokopwa kufikia wakati wa chakula cha mchana.
Kwa hivyo kufikia wakati wa chakula cha mchana, idadi ya vitabu vilivyosalia itakuwa 100-x
Baada ya kuongeza vitabu 40 zaidi, jumla ya vitabu iliongezeka kuwa 100-x+40
Ikiwa jumla ya vitabu vilivyokopwa katika maktaba kufikia jioni ilikuwa 30, jumla ya vitabu kwenye rafu baadaye ni 100-x+40-30 = 60
Hivyo 110 -x = 60
Hivyo x = 50 vitabu