$\displaystyle{18}{{c}}^{{2}}\usepackage{cmbright}\Huge\$ is a common factor, but is not the GCF. Also, this is an incorrect factorization. If you used the distributive property to multiply $\displaystyle{18}{{c}}^{{2}}{\left({2}{{c}}^{{3}}+{3}{{c}}^{{4}}\right)}\usepackage{cmbright}\Huge\$ , you would get $\displaystyle{36}{{c}}^{{5}}+{54}{{c}}^{{6}}\usepackage{cmbright}\Huge\$ , not $\displaystyle{36}{{c}}^{{5}}+{54}{{c}}^{{8}}\usepackage{cmbright}\Huge\$ .