#### Answer

$[0, 3 ]$

#### Work Step by Step

We are given:
$f(x)=\sqrt{x}+\sqrt{3-x}$
The domain of $\sqrt{x}$ is $[0,\ \infty)$.
The domain of $\sqrt{3-x}$ is $(-\infty, 3]$.
Therefore, the domain of $f(x)$ is the intersection of the two domains: $(-\infty,\ 3]\cap [0,\ \infty)=[0, 3 ]$