Remember f(x) is a 'machine' with a slot: x:
f(house) = 4*house - house^2! :)
f(4) = 4*4 -4^2 = 0
f(-4) =-16 - (-4)^2 = -32
f(4)-f(-4) = 32.
Alternative, f(x) -f(-x) = 4x -(4*(-x) ) = 8*x, because x^2-(-x)^2 = 0.
8*4=32. Just to show that part of your function f(x) is even (x^2) whereas the other part is odd (4*x)
