Given f(x)=-4x+8, verify if f(x)>4 then x>1?
We'll substitute f(x) by it's equation:
-4x+8 > 4
We'll isolate -4x to the left side subtracting 8 both sides:
-4x + 8 - 8 > 4 - 8
-4x > -4
We'll divide by -4 both sides changing the direction of inequality:
x < 1
We notice that if f(x) > 4, then x < 1, therefore the constraint given by enunciation is not true.