(x^3+x+1)×(y^3+y+1)=x^3y^3+x^3y+xy^3+x^3+xy+x+y^3+y+1
So that:
=(xy)^3+ xy(x^2+y^2)+xy+(x+y)+(x^3+y^3)+1
Now put xy=-2, and x+y=3:
=(-2)^3+ (-2)(x^2+y^2)+(-2)+3+(x^3+y^3)+1
=-8-2(x^2+y^2)-2+3+(x^3+y^3)+1
=-6-2(x^2+y^2)+(x^3+y^3)
Now to calculate x^2+y^2 use:
(x+y)^2=3^2
x^2+y^2+2xy=9
x^2+y^2+2(-2)=9
x^2+y^2-4=9
x^2+y^2=13
and:
x^3+y^3=(x+y)(x^2+y^2-xy)=3(13-(-2))=3(13+2)=3(15)=45
So that:
=-6-2(x^2+y^2)+(x^3+y^3)=-6-2(13)+45
=-6-26+45
=-32+45
(x^3+x+1)×(y^3+y+1)=13