Correct. The power property says: $\displaystyle{\log}_{{b}}{{M}}^{{n}}={n}\cdot{\log}_{{b}}{M}\usepackage{cmbright}\Huge\$

Therefore: $\displaystyle{\log}_{{{10}}}{{x}}^{{4}}={4}\cdot{\log}_{{{10}}}{x}\usepackage{cmbright}\Huge\$

The question mark stands for 4.