\[\boxed{\mathbf{830\ (830)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[\textbf{а)}\ a = 5,\ b = - 10:\]
\[2a - b = 2 \cdot 5 - ( - 10) = 10 - ( - 10) = 10 + 10 = 20.\]
\[\textbf{б)}\ a = - 6,\ b = 3:\]
\[ab - 60 = - 6 \cdot 3 - 60 = - 18 - 60 = - 18 + ( - 60) = - 78.\]
\[Ответ:\ \ а)\ 20;\ \ \ б) - 78.\]