3d Geometry

If the lines \({{x - k} \over 1} = {{y - 2} \over 2} = {{z - 3} \over 3}\) and
\({{x + 1} \over 3} = {{y + 2} \over 2} = {{z + 3} \over 1}\) are co-planar, then the value of k is _____________.