This is a factorization of the given expression, but $\displaystyle{8}{{z}}^{{2}}\usepackage{cmbright}\Huge\$ is not the GCF. You may have subtracted the exponents in the expression and so used $\displaystyle{{z}}^{{2}}\usepackage{cmbright}\Huge\$ as part of the GCF. To find the GCF of two terms, be sure to factor each term and locate all of the common factors. The correct answer is $\displaystyle{8}{{z}}^{{4}}{\left({7}+{9}{{z}}^{{2}}\right)}\usepackage{cmbright}\Huge\$ .