(-2ab+2a+3b)-(3ab+2b-2a)-(a+4b+ab)
=-2ab+2a+3b-3ab-2b+2a-a-4b-ab
=(-2ab-3ab-ab)+(2a+2a-a)+(3b-2b-4b)
=-6ab+3a-3b
=-6ab+3(a-b)
=-6+6
=0