4 The points \(A , B , C\) and \(D\) have coordinates \(( 2 , - 1,0 ) , ( 3,2,5 ) , ( 4,2,3 )\) and \(( - 1 , a , b )\) respectively, where \(a\) and \(b\) are constants.
- Find the angle \(A B C\).
- Given that the lines \(A B\) and \(C D\) are parallel, find the values of \(a\) and \(b\).