\(a,\left(12x^3y^3-3x^2y^3+4x^2y^4\right):6x^2y^3\)
\(=12x^3y^3:6x^2y^3-3x^2y^3:6x^2y^3+4x^2y^4:6x^2y^3\)
\(=2x-\frac{1}{2}+\frac{2}{3}y\)
\(b,\left(6x^3-19x^2+23x-12\right):\left(2x-3\right)\)
\(=\left(6x^3-10x^2+8x-9x^2+15x-12\right):\left(2x-3\right)\)
\(=\left(2x-3\right)\left(3x^2-5x+4\right):\left(2x-3\right)\)
\(=3x^2-5x+4\)