The equations of the lines l and m are given by

l: \(\mathbf{r} = \begin{pmatrix} 3 \\ -2 \\ 1 \end{pmatrix} + \lambda \begin{pmatrix} 1 \\ 1 \\ 2 \end{pmatrix}\) and m: \(\mathbf{r} = \begin{pmatrix} 6 \\ -3 \\ 6 \end{pmatrix} + \mu \begin{pmatrix} -2 \\ 4 \\ c \end{pmatrix}\),

where c is a positive constant. It is given that the angle between l and m is 60°.

(a) Find the value of c.

(b) Show that the length of the perpendicular from (6, -3, 6) to l is \(\sqrt{11}\).