The graph of $\displaystyle{y}={\log}_{{b}}{x}\usepackage{cmbright}\Huge\$ for any $\displaystyle{0}<{b}<{1}\usepackage{cmbright}\Huge\$ has this general shape. If $\displaystyle{b}>{1}\usepackage{cmbright}\Huge\$ , the graph of $\displaystyle{y}={\log}_{{b}}{x}\usepackage{cmbright}\Huge\$ would be increasing (the mirror image of the same shape around the x-axis). Because $\displaystyle{3}>{1}\usepackage{cmbright}\Huge\$ , the graph of $\displaystyle{y}={\log}_{{{3}}}{x}\usepackage{cmbright}\Huge\$ would be increasing, so it could not be the one shown.