Subtract 8 from all parts: $\displaystyle-{6}-{8}\le-{2}{k}+{8}-{8}\le{2}-{8}\usepackage{cmbright}\Huge\$

Simplify to: $\displaystyle-{14}\le-{2}{k}\le-{6}\usepackage{cmbright}\Huge\$

Divide all parts by $\displaystyle-{2}\usepackage{cmbright}\Huge\$ , and reverse the inequality signs.

$\displaystyle\frac{{-{14}}}{{-{{2}}}}\ge\frac{{-{2}{k}}}{{-{{2}}}}\ge\frac{{-{6}}}{{-{2}}}\usepackage{cmbright}\Huge\$ , so $\displaystyle{7}\geq{k}\geq{3}\usepackage{cmbright}\Huge\$ or $\displaystyle{3}\le{k}\le{7}\usepackage{cmbright}\Huge\$