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

### Instruction:
 一个三角形的周长是160厘米。如果两边分别是40厘米和50厘米，计算第三边的长度是多少？


### Response:
 要得到周长，你把所有的边加起来，所以o + 40 + 50 = 160
因此，o = 160 - 40 - 50
因此，第三边的长度是o = 70厘米。