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

### Instruction:
Angel has written letters to all of her pen pals and is putting all of the letters in envelopes. Most of the letters are put into large envelopes and the remaining 20 letters are put into small envelopes. The large envelopes each contain 2 letters each. If Angel has written a total of 80 letters, how many large envelopes did she use?

### Response:
 Kwa kuwa baadhi ya barua zimefungwa kwenye bahasha ndogo, lazima kuwe na jumla ya barua 80 - 20 barua kwenye bahasha ndogo = <<80-20=60>>60 barua kwenye bahasha kubwa.
Hivyo, Angel alitumia barua 60 / 2 barua kwa kila bahasha kubwa = <<60/2=30>>30 bahasha kubwa.