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

### Instruction:
 马克和彼得在他们的后院挖了池塘。马克的池塘比彼得的池塘深4英尺，是彼得池塘深度的3倍。如果马克的池塘深度为19英尺，彼得的池塘深度是多少？


### Response:
 让我们用p表示马克池塘的深度
3*p+4=19
3*p=19-4=15
3p=15
p=<<5=5>>5