9 The random variable \(X\) has probability distribution given by
$$\mathrm { P } ( X = x ) = a + b x \quad \text { for } x = 1,2 \text { and } 3 ,$$
where \(a\) and \(b\) are constants.
Show that \(3 a + 6 b = 1\).
Given that \(\mathrm { E } ( X ) = \frac { 5 } { 3 }\), find \(a\) and \(b\).