1)
You have a typo here.
2)
-4x - 2y = -1
-4x + 1 = 2y
2y = -4x + 1
y = -2x + (1/2)
f(x) = -2x + (1/2)
3)
6x - 5y = 1
5y = 6x - 1
y = (6/5)x - (1/5)
f(x) = (6/5)x - (1/5)
4)
-6x - 9y = 0
9y = -6x
y = (-6/9)x
y = (-2/3)x
f(x) = (-2/3)x
5)
-4x + 2y = 8
-2x + y = 4
y = 2x + 4
f(x) = 2x + 4