\[12xy^{2} - 4y^{2} + 3x^{2}y - xy =\]
\[= 4y^{2}(3x - 1) + xy(3x - 1) =\]
\[= (3x - 1)\left( 4y^{2} + xy \right) =\]
\[= y \cdot (3x - 1)(4y + x)\]