#### Answer

$\color{blue}{(-\infty, 9) \cup (9, +\infty)}$

#### Work Step by Step

RECALL:
The domain of the sum, difference, and product of $f(x)$ and $g(x)$ is the common elements of the domains of the two functions.
The domain of the respective functions are:
$f(x)$ is defined for all real numbers so its domain is: $(-\infty, +\infty)$
$g(x)$ is defined for all real numbers except 9 so its domain is: $(-\infty, 9) \cup (9, +\infty)$
Note that:
$(-\infty, +\infty) \cap [(-\infty, 9) \cup(9, +\infty)]
\\= (-\infty, 9) \cup (9, +\infty)$.
Thus, the domain of the sum, difference, and product of $f(x)$ and $g(x)$ is:
$\color{blue}{(-\infty, 9) \cup (9, +\infty)}$