Explanation:
all the functions with the "exponent" -1 mean inverse function (and not 1/function).
the inverse function gets a y value as input and delivers the corresponding x value as result.
so,

gets 0 as input y value. now, what was the x value in g(x) that delivered 0 ?
4
that x value delivering 0 as y was 4.
so,

the inverse function for a general, continuous function get get by transforming the original functional equation, so that x is calculated out of y :
h(x) = y = 4x + 13
y - 13 = 4x
x = (y - 13)/4
and now we rename x to y and y to x to make this a "normal" function :
y = (x - 13)/4
so,

a combined function (f○g)(x) means that we first calculate g(x) and then use that result as input value for f(x). and that result is then the final result.
formally, we simply use the functional expression of g(x) and put it into every occurrence of x in f(x).
so, we have here
4x + 13
that we use in the inverse function
((4x + 13) - 13)/4 = (4x + 13 - 13)/4 = 4x/4 = x
the combination of a function with its inverse function always delivers the input value x unchanged.
so,
(inverse function ○ function) (-3) = -3