You may have multiplied the first equation by 4 instead of by $\displaystyle-{4}\usepackage{cmbright}\Huge\$ and made a mistake combining it with the second equation. This ordered pair satisfies the second equation, but not the first. If you substitute it into the left side you will get $\displaystyle{2}{x}+{y}={2}{\left({7}\right)}-{5}={14}-{5}={9}\usepackage{cmbright}\Huge\$ , not 19.