Correct. Subtract 9 from both sides to isolate the radical: $\displaystyle\sqrt{{{8}{x}-{4}}}={6}\usepackage{cmbright}\Huge\$

Square both sides: $\displaystyle{{\left(\sqrt{{{8}{x}-{4}}}\right)}}^{{2}}={{6}}^{{2}}\usepackage{cmbright}\Huge\$

Simplify: $\displaystyle{8}{x}-{4}={36}\usepackage{cmbright}\Huge\$

Solve for x: $\displaystyle{8}{x}={40}\usepackage{cmbright}\Huge\$ , so $\displaystyle{x}={5}\usepackage{cmbright}\Huge\$