Substitute 5 for x and 4 for y.

$\displaystyle{2}{\left({5}\right)}-{4}{\left({4}\right)}=-{6}\usepackage{cmbright}\Huge\$ $\displaystyle{4}={5}+{1}\usepackage{cmbright}\Huge\$

$\displaystyle{10}-{16}=-{6}\usepackage{cmbright}\Huge\$ 4=6 False

$\displaystyle-{6}=-{6}\usepackage{cmbright}\Huge\$ True

For the ordered pair to be a solution to the system, it must make both equations true. It is not a solution.

$\displaystyle{2}{\left({5}\right)}-{4}{\left({4}\right)}=-{6}\usepackage{cmbright}\Huge\$	$\displaystyle{4}={5}+{1}\usepackage{cmbright}\Huge\$
$\displaystyle{10}-{16}=-{6}\usepackage{cmbright}\Huge\$	4=6 False
$\displaystyle-{6}=-{6}\usepackage{cmbright}\Huge\$ True