8. Referred to an origin \(O\), the points \(A , B\) and \(C\) have position vectors ( \(9 \mathbf { i } - 2 \mathbf { j } + \mathbf { k }\) ), \(( 6 \mathbf { i } + 2 \mathbf { j } + 6 \mathbf { k } )\) and \(( 3 \mathbf { i } + p \mathbf { j } + q \mathbf { k } )\) respectively, where \(p\) and \(q\) are constants.

1. Find, in vector form, an equation of the line \(l\) which passes through \(A\) and \(B\). Given that \(C\) lies on \(l\),
2. find the value of \(p\) and the value of \(q\),
3. calculate, in degrees, the acute angle between \(O C\) and \(A B\). The point \(D\) lies on \(A B\) and is such that \(O D\) is perpendicular to \(A B\).
4. Find the position vector of \(D\).