5 The polynomial \(3 x ^ { 3 } + 8 x ^ { 2 } + a x - 2\), where \(a\) is a constant, is denoted by \(\mathrm { p } ( x )\). It is given that \(( x + 2 )\) is a factor of \(\mathrm { p } ( x )\).
- Find the value of \(a\).
- When \(a\) has this value, solve the equation \(\mathrm { p } ( x ) = 0\).