\[\boxed{\mathbf{1098\ (1089)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ 3c - 3d = 3 \cdot (c - d)\]
\[2)\ mx - my = m(x - y)\]
\[3)\ 7a - 7b - 7c =\]
\[= 7 \cdot (a - b - c)\]
\[4) - 12x - 8y + 20 =\]
\[= - 4 \cdot (3x + 2y - 5)\]