$\begin{array}{1 1} -\;^6 \large C_r\;x^{12-2r} y^r \\ ^6 \large C_r\;x^{12-2r} y^r \\ -\;^6 \large C_r\;x^{6-r} y^r \\ ^6 \large C_r\;x^{12-2r} y^{6-r} \end{array} $