18(a+b)^3+2b(b-a)^2
=18(a^3+3a^2b+3ab^2+b^3)+2b(b^2-2ab+a^2)
=18a^3+54a^2b+54ab^2+18b^3+2b^3-4ab^2+2a^2b
=18a^3+56a^2b+50ab^2+20b^3