#### Answer

$5-x\gt0$

#### Work Step by Step

RECALL:
The domain of the function $y=\log_b{x}$ is $x \gt 0$.
This means that if $x$ is replaced by $5-x$ and $b=2$ to have the function $g(x)=\log_2{(5-x)}$, then the domain of this function can be found by solving the inequality
$5-x \gt 0$