Apply the section formula and preserve vertex order

The position vectors of vertices $A$, $B$ and $C$, relative to the origin $O$, are $-3\mathbf i+4\mathbf k$, $-2\mathbf i+4\mathbf j-3\mathbf k$ and $11\mathbf i-4\mathbf j-9\mathbf k$ respectively.

(i) Find a unit vector parallel to $\overrightarrow{OA}$.

(ii) A point $P$ divides $AC$ in the ratio $1:3$. Find the position vector of $P$.

(iii) Show that the points $O$, $B$ and $P$ are collinear.

(iv) $OBDC$ forms a parallelogram. Find the position vector of $D$.