Correct. The information gives you two equations:

$\displaystyle{x}-{y}={58}\usepackage{cmbright}\Huge\$ and $\displaystyle\frac{{{x}+{y}}}{{2}}={323}\usepackage{cmbright}\Huge\$

Multiply the second equation by 2: $\displaystyle{x}+{y}={646}\usepackage{cmbright}\Huge\$

Add this to $\displaystyle{x}-{y}={58}\usepackage{cmbright}\Huge\$ : $\displaystyle{2}{x}={704}\usepackage{cmbright}\Huge\$ , so $\displaystyle{x}={352}\usepackage{cmbright}\Huge\$

Substitute into the third equation: $\displaystyle{352}+{y}={646}\usepackage{cmbright}\Huge\$ , so $\displaystyle{y}={294}\usepackage{cmbright}\Huge\$