Answer
$f(x)= \frac{1}{x}$
And:
$g(x)=x+3$
Other answers are also possible.
Work Step by Step
We want: $G(x)=(f\circ g)(x)=f(g(x))$.
We make:
$f(x)= \frac{1}{x}$
And:
$g(x)=x+3$
Then:
$f(g(x))=\frac{1}{x+3}=G(x)$
Other answers are also possible.