2x^2y+[2xy-[3x^2y-2[2xy-3xy^2]]-4xy^2]
=2x^2y+[2xy-[3x^2y-4xy+6xy^2]-4xy^2]
=2x^2y+[2xy-3x^2y+4xy-6xy^2-4xy^2]
=2x^2y+[6xy-3x^2y-10xy^2]
=2x^2y+6xy-3x^2y-10xy^2
=6xy-x^2y-10xy^2
=xy(6-x-10y)
=-1*(6-1+10)
=-1*15
=-15