3a^2-(4a^2b-2ab^2-b^2)-(2ab^2+3a^2-3b^2)+3a^2b
=3a^2-4a^2b+2ab^2+b^2-2ab^2-3a^2+3b^2+3a^2b
=4b^2-a^2b
a=-4,b=4
4b^2-a^2b
=4*4^2-(-4)^2*4
=4*16-16*4
=0