(3-9b^2)-(b^3-6b+7)=
15y^3-(3y-2)(5y-1)=
15y^3-(3y-2)(5y-1)=15y^3-(15y^2-3y-10y+2)= 15y^3-15y^3+3y+10y-2= 13y-2
(3-9b^2)-(b^3-6b+7)=
3-9b^2-b^3+6b-7= 3-8b^3+6b-7= 8b^3+6b-415y^3-(3y-2)(5y-1)=
15y^3-(3y-2)(5y-1)=15y^3-(15y^2-3y-10y+2)= 15y^3-15y^3+3y+10y-2= 13y-2