#### Answer

$\text{all real numbers}$

#### Work Step by Step

$\bf{\text{Solution Outline:}}$
The domain of the given rational function, $
R(n)=\dfrac{3n+5}{9n^2+25}
,$ are the values of $
n
$ which will NOT make the denominator equal to $0.$
$\bf{\text{Solution Details:}}$
The denominator, $9n^2+25,$ is always a positive number for any value of $
n
$ since $n$ is squared.
Hence, the domain is the set of $
\text{all real numbers}
.$