Solve the second equation for x: $\displaystyle{x}={14}+{5}{y}\usepackage{cmbright}\Huge\$

Substitute $\displaystyle{14}+{5}{y}\usepackage{cmbright}\Huge\$ for x in the first equation: $\displaystyle{4}{\left({14}+{5}{y}\right)}+{2}{y}={34}\usepackage{cmbright}\Huge\$

Simplify: $\displaystyle{56}+{20}{y}+{2}{y}={34}\usepackage{cmbright}\Huge\$ or $\displaystyle{56}+{22}{y}={34}\usepackage{cmbright}\Huge\$

Solve for y: $\displaystyle{22}{y}=-{22}\usepackage{cmbright}\Huge\$ , so $\displaystyle{y}=-{1}\usepackage{cmbright}\Huge\$

Substitute this value for y into the equation you started with: $\displaystyle{x}={14}+{5}{\left(-{1}\right)}={14}-{5}={9}\usepackage{cmbright}\Huge\$