Answer
The domain is the set of real numbers less than or equal to $0$.
Work Step by Step
The given function is
$y=4+\sqrt{-x}$
The radicand cannot be negative.
So, $-x$ is greater than or equal to zero.
$\Rightarrow -x\geq 0$
Multiply each side by $-1$ and reverse the inequality symbol.
$\Rightarrow x\leq 0$
Hence, the domain is the set of real numbers less than or equal to $0$.
