10 The position vectors of the points \(A , B , C , D\) are
$$\mathbf { i } + \mathbf { j } + 3 \mathbf { k } , \quad 3 \mathbf { i } + 4 \mathbf { j } + 5 \mathbf { k } , \quad - \mathbf { i } + 3 \mathbf { k } , \quad m \mathbf { j } + 4 \mathbf { k } ,$$
respectively, where \(m\) is a constant.
- Show that the lines \(A B\) and \(C D\) are parallel when \(m = \frac { 3 } { 2 }\).
- Given that \(m \neq \frac { 3 } { 2 }\), find the shortest distance between the lines \(A B\) and \(C D\).
- When \(m = 2\), find the acute angle between the planes \(A B C\) and \(A B D\), giving your answer in degrees.