2ab^2+3ba^2+6a^2b-8b^2a-4ab-6+7a
=2ab^2+3a^2b+6a^2b-8ab^2-4ab-6+7a
=(2-8)ab^2+(3+6)a^2b-4ab+7a-6
=-6ab^2+9a^2b-4ab+7a-6