Incorrect.

$\displaystyle{y}={\log}_{{{3}}}{243}\usepackage{cmbright}\Huge\$ is equivalent to $\displaystyle{{3}}^{{y}}={243}\usepackage{cmbright}\Huge\$ . Try computing different powers of 3: $\displaystyle{{3}}^{{2}},{{3}}^{{3}},{{3}}^{{4}},{{3}}^{{5}}\usepackage{cmbright}\Huge\$ .