Substitute the expression $\displaystyle{\left({x}-{1}\right)}\usepackage{cmbright}\Huge\$ into the function for x: $\displaystyle{f{{\left({x}-{1}\right)}}}={3}{\left({x}-{1}\right)}-{5}\usepackage{cmbright}\Huge\$

Use the distributive property on the right side: $\displaystyle{f{{\left({x}-{1}\right)}}}={3}{x}-{3}-{5}\usepackage{cmbright}\Huge\$

Combine like terms to simplify: $\displaystyle{f{{\left({x}-{1}\right)}}}={3}{x}-{8}\usepackage{cmbright}\Huge\$