9 Relative to an origin \(O\), the position vectors of the points \(A , B , C\) and \(D\) are given by
$$\overrightarrow { O A } = \left( \begin{array} { r }
1 \\
3 \\
- 1
\end{array} \right) , \quad \overrightarrow { O B } = \left( \begin{array} { r }
3 \\
- 1 \\
3
\end{array} \right) , \quad \overrightarrow { O C } = \left( \begin{array} { l }
4 \\
2 \\
p
\end{array} \right) \quad \text { and } \quad \overrightarrow { O D } = \left( \begin{array} { r }
- 1 \\
0 \\
q
\end{array} \right) ,$$
where \(p\) and \(q\) are constants. Find
- the unit vector in the direction of \(\overrightarrow { A B }\),
- the value of \(p\) for which angle \(A O C = 90 ^ { \circ }\),
- the values of \(q\) for which the length of \(\overrightarrow { A D }\) is 7 units.