Incorrect. The correct system is:

$\displaystyle{a}+{4}{c}={34}\usepackage{cmbright}\Huge\$

$\displaystyle{2}{a}+{2}{s}={28}\usepackage{cmbright}\Huge\$

$\displaystyle{2}{c}={3}{s}\usepackage{cmbright}\Huge\$ , or $\displaystyle{2}{c}-{3}{s}={0}\usepackage{cmbright}\Huge\$

Multiply the first equation by $\displaystyle-{2}\usepackage{cmbright}\Huge\$ and add it to the second equation to eliminate a. Together with the third equation, you have a system of two equations and two variables. The correct answer = 10.