(1)-9y+6x²+3(y-2x²/3)
=-9y+6x²+3y-2x²
=4x²-6y
(2)5(a²b-3ab²)-2(a²b-7ab²)
=5a²b-15ab²-2a²b+14ab²
=3a²b-ab²
=ab(3a-b)
(3)3x²-[7x-(4x-3)-2x²]
=3x²-(7x-4x+3-2x²)
=3x²-(3x+3-2x²)
=3x²-3x-3+2x²
=5x²-3x-3