You may have chosen this answer because there are nines in all three equations. However, $\displaystyle{{b}}^{{y}}={x}\usepackage{cmbright}\Huge\$ is equivalent to $\displaystyle{\log}_{{{b}}}{x}={y}\usepackage{cmbright}\Huge\$ . This means that $\displaystyle{b}={9}\usepackage{cmbright}\Huge\$ when the base of the exponential equation is 9.