7. A curve has the equation
$$y = x ^ { 3 } + a x ^ { 2 } - 15 x + b$$
where \(a\) and \(b\) are constants.
Given that the curve is stationary at the point \(( - 1,12 )\),
- find the values of \(a\) and \(b\),
- find the coordinates of the other stationary point of the curve.