Correct. This expression is a perfect square trinomial because $\displaystyle{{x}}^{{2}}={x}\cdot{x}\usepackage{cmbright}\Huge\$ , $\displaystyle{16}={4}\cdot{4}\usepackage{cmbright}\Huge\$ , and $\displaystyle{8}{x}={2}\cdot{x}\cdot{4}\usepackage{cmbright}\Huge\$ . Therefore, $\displaystyle{{x}}^{{2}}+{8}{x}+{16}={{\left({x}+{4}\right)}}^{{2}}\usepackage{cmbright}\Huge\$ . The missing number is 4.