3x^2 y+{xy-[3x^2 y-(4xy^2 +1/2xy)]-(4x^2 y+3/2xy)}
=3x²y+{xy-[3x²y-4xy²-1/2xy]-4x²y-3/2xy}
=3x²y+{xy-3x²y+4xy²+1/2xy-4x²y-3/2xy}
=3x²y+xy-3x²y+4xy²+1/2xy-4x²y-3/2xy
=4xy²-4x²y