Incorrect. Use the power property: $\displaystyle{\log}_{{b}}{{M}}^{{n}}={n}\cdot{\log}_{{b}}{M}\usepackage{cmbright}\Huge\$

$\displaystyle{\log}_{{{2}}}{{8}}^{{4}}={4}\cdot{\log}_{{{2}}}{8}\usepackage{cmbright}\Huge\$

Then use the definition of logarithm.