Correct. Use the quotient property: $\displaystyle{\log}_{{b}}\frac{{M}}{{N}}={\log}_{{b}}{M}-{\log}_{{b}}{N}\usepackage{cmbright}\Huge\$

$\displaystyle{\log}_{{{5}}}{\left(\frac{{y}}{{125}}\right)}={\log}_{{{5}}}{y}-{\log}_{{{5}}}{125}\usepackage{cmbright}\Huge\$

Now $\displaystyle{125}={{5}}^{{3}}\usepackage{cmbright}\Huge\$ , so $\displaystyle{\log}_{{5}}{125}={3}\usepackage{cmbright}\Huge\$ . The ? represents the integer 3.