6. The circle \(C\) has the equation
$$x ^ { 2 } + y ^ { 2 } - 12 x + 8 y + 16 = 0 .$$
- Find the coordinates of the centre of \(C\).
- Find the radius of \(C\).
- Sketch C.
Given that \(C\) crosses the \(x\)-axis at the points \(A\) and \(B\),
- find the length \(A B\), giving your answer in the form \(k \sqrt { 5 }\).