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? Let's answer step by step:
Let B be the cost of the blue socks. 4 * 3 + 6 * Y = 42. 12 + 6 * Y = 42. 6 * Y = 30. Y = 5. The answer: 5.