You would plug in 4 for x and 8 for y giving you,
2(4) + 7(8) = 1
8 = 4(4) - 8
Now multiply the number together getting,
8 + 56 = 1
8 = 16 - 8
Now add/subtract,
64=1
8=8
While the second equation is true, the first is not. This would make (4,8) not a solution to the system.