Find the range of the quadratic function $\displaystyle{f{{\left({x}\right)}}}=-{8}{{x}}^{{2}}-{48}{x}-{60}\usepackage{cmbright}\Huge\$ .

The range is all real numbers $\displaystyle{f{{\left({x}\right)}}}\usepackage{cmbright}\Huge\$ such that $\displaystyle{f{{\left({x}\right)}}}\le\usepackage{cmbright}\Huge\$ _____.