Раскройте скобки: 8*(3с+7d) , (3-2b)*7
8*(3с+7d)=8*3c+8*7d=24c+56d
(3-2b)*7=3*7-2b*7=21-14b
8*(3с+7d)=24c+56d
(3-2d)*7=21-14d