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

### Instruction:
 约翰从海拔400英尺开始。他以每分钟下降10英尺的速度下降了5分钟。他现在的海拔是多少？


### Response:
 他下降了10*5=<<10*5=50>>50英尺。
所以他现在的海拔是400-50=<<400-50=350>>350英尺。