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

### 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:
 จำนวนเงินรวมที่เอแวนมีคือ 1 + 12 = $<<1+12=13>>13.
ดังนั้นเอแวนต้องการเงินเพิ่มอีก 20 - 13 = $<<20-13=7>>7.