А)18с^2 - 2(9с^2-6с+1)= 18с^2- 18с^2+12с-2= 12с-2
Б)2а^2-6а+3а-9-8а+12а^2= 14а^2-11а-9
21- 14 = 7
15-8 = 7
85-78 = 7
158-151=7
14-7=7