3x²-[7x-(4x-3)-3x²]
=3x²-(7x-4x+3-3x²)
=3x²-(3x+3-3x²)
=3x²-3x-3+3x²
=6x²-3x-3
=3(2x²-x-1)
=3(2x+1)(x-1)