6 The coordinates of points \(A\) and \(B\) are \(( - 3 k - 1 , k + 3 )\) and \(( k + 3,3 k + 5 )\) respectively, where \(k\) is a constant ( \(k \neq - 1\) ).
- Find and simplify the gradient of \(A B\), showing that it is independent of \(k\).
- Find and simplify the equation of the perpendicular bisector of \(A B\).