Answer
$5z(z+9)$.
Work Step by Step
The given expression is
$=5z^2+45z$
The GCF of $5$ and $45$ is $5$.
The GCF of $z^2$ and $z$ is $z$.
So, the greatest common monomial factor of the terms is $5z$.
Hence, the factor form is $5z(z+9)$.