6. The curve \(C\) has equation
$$16 y ^ { 3 } + 9 x ^ { 2 } y - 54 x = 0$$
- Find \(\frac { \mathrm { d } y } { \mathrm {~d} x }\) in terms of \(x\) and \(y\).
- Find the coordinates of the points on \(C\) where \(\frac { \mathrm { d } y } { \mathrm {~d} x } = 0\)