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

### Instruction:
 路易斯需要买一些袜子。他买了4双红袜子和6双蓝袜子。总共花了42美元。如果红袜子每双3美元，他每双蓝袜子花了多少钱？


### Response:
 4双红袜子花费了4*$3=$<<4*3=12>>12
设X为蓝袜子的价格
6*X=$30
X=$<<5=5>>5