If \( \vec{a}, \vec{b}, \vec{c} \) are non-coplanar vectors and the points
\[
\lambda \vec{a} + 3\vec{b} - \vec{c}, \quad \vec{a} - \lambda \vec{b} + 3\vec{c}, \quad
3\vec{a} + 4\vec{b} - \lambda \vec{c}, \quad \vec{a} - 6\vec{b} + 6\vec{c}
\]
are coplanar, then one of the values of \( \lambda \) is: