The equation $\displaystyle{{b}}^{{y}}={x}\usepackage{cmbright}\Huge\$ is equivalent to $\displaystyle{\log}_{{{b}}}{x}={y}\usepackage{cmbright}\Huge\$ , so $\displaystyle{b}={4}\usepackage{cmbright}\Huge\$ , $\displaystyle{y}=-{2}\usepackage{cmbright}\Huge\$ , and $\displaystyle{x}=\frac{{1}}{{16}}\usepackage{cmbright}\Huge\$ .

Substitute these values into the logarithmic equation and you have: $\displaystyle{\log}_{{{4}}}{\left(\frac{{1}}{{16}}\right)}=-{2}\usepackage{cmbright}\Huge\$