Substitute $\displaystyle{2}+{7}{x}\usepackage{cmbright}\Huge\$ for y in the second equation: $\displaystyle-{2}{x}+{6}{\left({2}+{7}{x}\right)}=-{28}\usepackage{cmbright}\Huge\$

Simplify: $\displaystyle-{2}{x}+{12}+{42}{x}=-{28}\usepackage{cmbright}\Huge\$ or $\displaystyle{12}+{40}{x}=-{28}\usepackage{cmbright}\Huge\$

Solve for x: $\displaystyle{40}{x}=-{40}\usepackage{cmbright}\Huge\$ , so $\displaystyle{x}=-{1}\usepackage{cmbright}\Huge\$

Substitute this value for x back into the first equation: $\displaystyle{y}={2}+{7}{\left(-{1}\right)}={2}-{7}=-{5}\usepackage{cmbright}\Huge\$