x + y = 1 from this: x = 1 - y
4x + y = -23
Substitute x = 1 - y into the second equation.
4x + y = -23
4*(1 - y) + y = -23
4 - 4y + y = -23
4 + y - 4y = -23
4 - 3y = -23
-3y = -23 - 4
-3y = -27
y = -27/-3
y = 9
Recall: x = 1 - y, substituting y = 9
x = 1 - 9
x = -8
x = -8, y = 9
