The axis of symmetry (a.o.s.) can be found in the following ways:
If the vertex is (h, k), then the a.o.s equation is x = h.
If the standard form of

, then the a.o.s. equation is

.
If the x-intercepts

and

are given, then the a.o.s equation is

Therefore,
f(x) has a.o.s of x = 4
g(x) has a.o.s of

⇒

h(x) has a.o.s. of

↔ there are multiple ways to find this
RANKING FUNCTIONS from smallest a.o.s value to greatest: h(x), g(x), f(x)