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

### Instruction:
 David alipata $12 barabarani. Kisha akampa rafiki yake Evan ambaye ana $1 na alihitaji kununua saa yenye thamani ya $20. Evan anahitaji kiasi gani zaidi?


### Response:
 David na Evan wana jumla ya $12 + $1 = $<<12+1=13>>13.
Saa inagharimu $20, hivyo Evan anahitaji $20 - $13 = $<<20-13=7>>7 zaidi.