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

### Instruction:
 杰瑞还清了一些债务。两个月前，他支付了12美元，而上个月，他支付了比前一个月多3美元。如果他的债务总共是50美元，他还需要支付多少？


### Response:
 12 + 3 = 15
50 - 15 = 35