#### Answer

$g; \text{ }f(x)$

#### Work Step by Step

RECALL:
The composition function $g \circ f$ is defined as:
$(g \circ f)(x) = g(f(x))$
This means that all the $x's$ in $g$ have to be replaced with $f(x)$.
Thus, the missing expressions in the given statement are:
$g; \text{ }f(x)$