You may have correctly factored $\displaystyle\sqrt{{{54}}}\usepackage{cmbright}\Huge\$ as $\displaystyle\sqrt{{{6}}}\cdot\sqrt{{{{3}}^{{2}}}}\usepackage{cmbright}\Huge\$ , but while taking the square root of $\displaystyle{{3}}^{{2}}\usepackage{cmbright}\Huge\$ , you mixed up the places of 3 and 6.