The Change of Base formula is $\displaystyle{\log}_{{{b}}}{x}=\frac{{{\log}_{{{a}}}{x}}}{{{\log}_{{{a}}}{b}}}.\usepackage{cmbright}\Huge\$

Using a new base of 10, you can rewrite $\displaystyle{\log}_{{{6}}}{58}\usepackage{cmbright}\Huge\$ as $\displaystyle\frac{{\log{{58}}}}{{\log{{6}}}}.\usepackage{cmbright}\Huge\$

You can then use a calculator to evaluate the quotient.