4. The circle \(C\) has equation
$$x ^ { 2 } + y ^ { 2 } + 4 x - 2 y - 11 = 0$$
Find
- the coordinates of the centre of \(C\),
- the radius of \(C\),
- the coordinates of the points where \(C\) crosses the \(y\)-axis, giving your answers as simplified surds.