(a-2b)³-(a+b)²*(a-8b)=a³-2a²b+4ab²-8b³-(a²+2ab+b²)*(a-8b)=
=a³-6a²b+12ab²-8b³-a³-2a²b-ab²+8a²b+16ab²+8b³=
(a³-a³)+(-6a²b-2a²b+8a²b)+(12ab²-ab²+16ab²)+(-8b³+8b³)≡27ab².
..............................
B=7+5=12. b^2=144,144/7=20 остаток 4,b^4=20736,20736/7=2962 остаток 2