Incorrect. The correct system is:

$\displaystyle{2}{a}+{3}{c}={28}\usepackage{cmbright}\Huge\$

$\displaystyle{a}+{c}+{2}{s}={22}\usepackage{cmbright}\Huge\$

$\displaystyle{s}={c}+{1}\usepackage{cmbright}\Huge\$ , or $\displaystyle-{c}+{s}={1}\usepackage{cmbright}\Huge\$

Multiply the third equation by $\displaystyle-{2}\usepackage{cmbright}\Huge\$ and add it to the second equation to eliminate s. Together with the first equation you have a system of two equations and two variables. The correct answer is 8.