You may have remembered that when you use the power property, the exponent becomes a factor. However, the exponent should be multiplied by the logarithm.

The expression $\displaystyle{\log}_{{{7}}}{{7}}^{{x}}\usepackage{cmbright}\Huge\$ simplifies to $\displaystyle{x}{\log}_{{{7}}}{7}\usepackage{cmbright}\Huge\$ .

You will then need to simplify $\displaystyle{\log}_{{{7}}}{7}\usepackage{cmbright}\Huge\$ .