Substitute $\displaystyle-{4}\usepackage{cmbright}\Huge\$ for x: $\displaystyle-{5}{{x}}^{{4}}=-{5}{{\left(-{4}\right)}}^{{4}}\usepackage{cmbright}\Huge\$ . Remember that a negative number raised to the fourth power equals a positive number. The correct answer is $\displaystyle-{1},{280}\usepackage{cmbright}\Huge\$ .