The base $\displaystyle{b}={4}\usepackage{cmbright}\Huge\$ , the exponent $\displaystyle{y}=-{4}\usepackage{cmbright}\Huge\$ , and $\displaystyle{x}=\frac{{1}}{{256}}\usepackage{cmbright}\Huge\$ , so: $\displaystyle{{4}}^{{-{4}}}=\frac{{1}}{{256}}\usepackage{cmbright}\Huge\$