\[\boxed{\mathbf{789\ (789)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[m = - 4;\ \ n = 5:\]
\[mn = - 4 \bullet 5 = - 20.\]
\[mn - 10 = - 20 - 10 = - 30.\]
\[- 2mn = - 2 \bullet ( - 20) = 2 \bullet 20 = 40.\]
\[Ответ:\ - 20;\ - 30;40.\]