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

### Instruction:
David found $12 on the street. He then gave it to his friend Evan who has $1 and needed to buy a watch worth $20. How much does Evan still need?

### Response:
David and Evan have a total of $12 + $1 = $<<12+1=13>>13.
The watch costs $20, so Evan still needs $20 - $13 = $<<20-13=7>>7.
#### 7