You substituted the expression $\displaystyle{\left({x}-{1}\right)}\usepackage{cmbright}\Huge\$ for the entire term $\displaystyle{3}{x}\usepackage{cmbright}\Huge\$ , instead of just for x. Your first step should be to replace x by $\displaystyle{\left({x}-{1}\right)}\usepackage{cmbright}\Huge\$ : $\displaystyle{f{{\left({x}-{1}\right)}}}={3}{\left({x}-{1}\right)}-{5}\usepackage{cmbright}\Huge\$ . Then simplify this expression.