This is a solution to the second equation, but not to the system. If you substitute these values into the first equation you get $\displaystyle{5}{\left(-{1}\right)}-{7}{\left({6}\right)}=-{9}\usepackage{cmbright}\Huge\$ , or $\displaystyle-{5}-{42}=-{9}\usepackage{cmbright}\Huge\$ , which is false. Substitute $\displaystyle{4}-{2}{y}\usepackage{cmbright}\Huge\$ for x in the first equation and solve for y. Substitute this value into any equation to find x.