Opposite sides of a parallelogram have the same lengths, so use the formula $\displaystyle{P}={2}{l}+{2}{w}\usepackage{cmbright}\Huge\$ to find the perimeter.

$\displaystyle{P}={2}{\left({8}\right)}+{2}{\left({6}\right)}={16}+{12}={28}\usepackage{cmbright}\Huge\$