You may have correctly simplified $\displaystyle{\log}_{{{6}}}{{\left({6}{x}\right)}}^{{2}}\usepackage{cmbright}\Huge\$ to $\displaystyle{2}\cdot{\log}_{{{6}}}{6}{x}\usepackage{cmbright}\Huge\$ . You also may have correctly simplified $\displaystyle{\log}_{{6}}{6}{x}\usepackage{cmbright}\Huge\$ to $\displaystyle{\log}_{{{6}}}{6}+{\log}_{{{6}}}{x}\usepackage{cmbright}\Huge\$ . However, this entire last expression should be multiplied by 2. You multiplied only the first term by 2.