You may have mixed up the values of x and y when substituting them into the equation.

$\displaystyle{3}+{3}{\left(-{1}\right)}={0}\usepackage{cmbright}\Huge\$ or $\displaystyle{3}-{3}={0}\usepackage{cmbright}\Huge\$ or $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$

The statement is true, so the ordered pair $\displaystyle{\left({3},-{1}\right)}\usepackage{cmbright}\Huge\$ is a solution to the equation.

The correct answer is $\displaystyle{4}{x}={8}{y}+{4}\usepackage{cmbright}\Huge\$ .