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

### Instruction:
Luis needed to buy some socks. He bought 4 pairs of red socks and 6 pairs of blue ones. In total, he spent $42. If the red socks cost $3 each, how much did he pay for each blue pair?

### Response:
 ให้ B เป็นราคาของถุงเท้าสีน้ำเงิน
4*3 +6*Y =42.
12 + 6*Y=42.
6*Y =30.
Y = <<5=5>>5.