You found the GCF of the two terms, but then it appears that you subtracted 2 from the two constants. If you used the distributive property to multiply $\displaystyle{2}{\left({12}{{n}}^{{3}}+{14}\right)}\usepackage{cmbright}\Huge\$ , you would get $\displaystyle{24}{{n}}^{{3}}+{28}\usepackage{cmbright}\Huge\$ , not $\displaystyle{14}{{n}}^{{3}}+{16}\usepackage{cmbright}\Huge\$ .