Note that $\displaystyle{{\left({{a}}^{{-{{3}}}}\right)}}^{{2}}={{a}}^{{-{3}{\left({2}\right)}}}\usepackage{cmbright}\Huge\$ . Also, remember that $\displaystyle{{c}}^{{0}}={1}\usepackage{cmbright}\Huge\$ . Does this help you simplify the expression?