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

### Instruction:
Tina is getting $20 for each book she sells. If she realizes a $120 profit on her sales, how many people have she sold the books to if each book costs $5 to make and every customer buys 2 at a time?

### Response:
 Kwanza tunahitaji kujua faida kwa kila kitabu. Ili kufanya hivyo, tunafanya 20-5=<<20-5=15>>15 dola kwa faida kwa kila kitabu.
Kisha tunahitaji kujua idadi ya jumla ya vitabu vilivyouzwa. Ili kufanya hivyo, tunafanya 120/15=<<120/15=8>>8 vitabu vilivyouzwa jumla.
Kwa kuwa vitabu vinauzwa 2 kwa wakati mmoja, tunagawanya idadi ya jumla ya vitabu vilivyouzwa na 2 ili kupata idadi ya jumla ya watu walionunua, tukifanya 8/2=4 watu jumla.