4. (a) Differentiate with respect to \(x\)
- \(x ^ { 2 } \mathrm { e } ^ { 3 x + 2 }\),
- \(\frac { \cos \left( 2 x ^ { 3 } \right) } { 3 x }\).
(b) Given that \(x = 4 \sin ( 2 y + 6 )\), find \(\frac { \mathrm { d } y } { \mathrm {~d} x }\) in terms of \(x\).