Multiply both sides by the common denominator 6:

$\displaystyle{6}\cdot\frac{{{x}-{4}}}{{3}}=\frac{{x}}{{6}}\cdot{6}\usepackage{cmbright}\Huge\$

$\displaystyle\frac{{6}}{{3}}\cdot{\left({x}-{4}\right)}={x}\cdot\frac{{6}}{{6}}\usepackage{cmbright}\Huge\$

$\displaystyle{2}{\left({x}-{4}\right)}={x}\usepackage{cmbright}\Huge\$ or $\displaystyle{2}{x}-{8}={x}\usepackage{cmbright}\Huge\$

$\displaystyle{x}-{8}={0}\usepackage{cmbright}\Huge\$ , so $\displaystyle{x}={8}\usepackage{cmbright}\Huge\$