Correct. Let a, c, and s be the cost for one adult, child, and senior. Then:

$\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: $\displaystyle-{8}{c}+{2}{s}=-{40}\usepackage{cmbright}\Huge\$

Multiply the third equation by 4 and add it to this: $\displaystyle-{10}{s}=-{40}\usepackage{cmbright}\Huge\$ , so $\displaystyle{s}={4}\usepackage{cmbright}\Huge\$

Substitute into the second to find $\displaystyle{a}={10}\usepackage{cmbright}\Huge\$ , and then into the third to find $\displaystyle{c}={6}\usepackage{cmbright}\Huge\$ .