\[\left( 6x^{2} - 4xy - y^{2} \right) - (*) = 4x^{2} + y^{2}\]
\[(*) = 6x^{2} - 4xy - y^{2} - 4x^{2} - y^{2}\]
\[(*) = 2x^{2} - 4xy - 2y^{2}.\]