10 The equations of the lines \(l\) and \(m\) are given by
$$l : \mathbf { r } = \left( \begin{array} { r }
3
- 2
1
\end{array} \right) + \lambda \left( \begin{array} { l }
1
1
2
\end{array} \right) \quad \text { and } \quad m : \mathbf { r } = \left( \begin{array} { r }
6
- 3
6
\end{array} \right) + \mu \left( \begin{array} { r }
- 2
4
c
\end{array} \right)$$
where \(c\) is a positive constant. It is given that the angle between \(l\) and \(m\) is \(60 ^ { \circ }\).
- Find the value of \(c\).
- Show that the length of the perpendicular from \(( 6 , - 3,6 )\) to \(l\) is \(\sqrt { 11 }\).