x - y = 8
Add y to both sides
x = 8 + y
4x + y = 4
Substitute the value of x from the first equation in
4(8 + y) + y = 4
Simplify and solve
32 + 4y + y = 4
32 + 5y = 4
5y = -28
y = -5.6
Now put that value of y into the first equation
x = 8 + (-5.6)
x = 2.4