This is a factorization of the given expression, but $\displaystyle{2}{{z}}^{{4}}\usepackage{cmbright}\Huge\$ is not the GCF. The GCF includes all the factors that the two terms have in common. The factor 2 occurs three times in each term. The correct answer is $\displaystyle{8}{{z}}^{{4}}{\left({7}+{9}{{z}}^{{2}}\right)}\usepackage{cmbright}\Huge\$ .