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

### Instruction:
Jake agrees to work part of his debt off.  He owed someone $100 but paid them $40 before agreeing to work off the rest.   He worked for $15 an hour.  How many hours did he have to work?

### Response:
 เขาต้องทำงานเพื่อชำระเงินที่เหลือ $100-$40=$<<100-40=60>>60.
ดังนั้นเขาต้องทำงาน $60/15=<<60/15=4>>4 ชั่วโมง.