Correct. Because A is 10,000 times as large as $\displaystyle{A}_{{0}}\usepackage{cmbright}\Huge\$ , $\displaystyle{A}={10},{000}{A}_{{0}}\usepackage{cmbright}\Huge\$ . Substitute this expression in for A.

$\displaystyle{R}={\log{{\left(\frac{{{10},{000}{A}_{{0}}}}{{A}_{{0}}}\right)}}}={\log{{10}}},{000}\usepackage{cmbright}\Huge\$

Now $\displaystyle{{10}}^{{4}}={10},{000}\usepackage{cmbright}\Huge\$ , so $\displaystyle{\log{{10}}},{000}={4}\usepackage{cmbright}\Huge\$ and $\displaystyle{R}={4}\usepackage{cmbright}\Huge\$ .