Correct. This expression is a perfect square trinomial because $\displaystyle{{x}}^{{2}}={x}\cdot{x}\usepackage{cmbright}\Huge\$ , $\displaystyle{36}={6}\cdot{6}\usepackage{cmbright}\Huge\$ , and $\displaystyle{12}{x}={2}\cdot{x}\cdot{6}\usepackage{cmbright}\Huge\$ . Therefore, $\displaystyle{{x}}^{{2}}+{12}{x}+{36}={{\left({x}+{6}\right)}}^{{2}}\usepackage{cmbright}\Huge\$ . The missing number is 6.