$\displaystyle{4}{\left({2}{x}-{1}\right)}={4}{\left({2}{x}\right)}-{4}{\left({1}\right)}={8}{x}-{4}\usepackage{cmbright}\Huge\$ . Substitute 6 for $\displaystyle{x}\usepackage{cmbright}\Huge\$ :
$\displaystyle{8}{\left({6}\right)}-{4}={48}-{4}={44}\usepackage{cmbright}\Huge\$