Multiply the coefficients of i together, and remember that $\displaystyle{{i}}^{{2}}=-{1}\usepackage{cmbright}\Huge\$ .

$\displaystyle{\left(-{11}{i}\right)}{\left({8}{i}\right)}={\left(-{11}\right)}{\left({8}\right)}{\left({i}\right)}{\left({i}\right)}={\left(-{88}\right)}{\left({{i}}^{{2}}\right)}={\left(-{88}\right)}{\left(-{1}\right)}={88}\usepackage{cmbright}\Huge\$