Answer
$\color{blue}{\dfrac{3z+x}{z^2}}$
Work Step by Step
The expressions are not similar since they have different denominators.
Make the expressions similar using their LCD which is $z^2$ to obtain:
$=\dfrac{3\color{red}{(z)}}{z\color{red}{(z)}}+\dfrac{x}{z^2}
\\=\dfrac{3z}{z^2}+\dfrac{x}{z^2}
\\=\color{blue}{\dfrac{3z+x}{z^2}}$
