Answer
$z^{2}(m+n)^{4}$
Work Step by Step
The greatest common factor of a group of terms is the greatest factor that evenly divides into all terms in the group.
In this case, $z^{2}(m+n)^{4}$ is the greatest common factor, because it is the largest factor that divides evenly into both terms.
$7z^{2}(m+n)^{4}\div z^{2}(m+n)^{4}=7$
$9z^{3}(m+n)^{5}\div z^{2}(m+n)^{4}=9z(m+n)$
