You probably switched the values of x and y.

If you substitute these values correctly you get: $\displaystyle{2}{\left({0}\right)}+{6}{\left(-{3}\right)}=-{6}\usepackage{cmbright}\Huge\$

Simplify: $\displaystyle{0}-{18}=-{18}\usepackage{cmbright}\Huge\$ or $\displaystyle-{18}=-{6}\usepackage{cmbright}\Huge\$

This is not a true statement, so the ordered pair $\displaystyle{\left({0},-{3}\right)}\usepackage{cmbright}\Huge\$ is not a solution to the equation.