4. A sequence \(a _ { 1 } , a _ { 2 } , a _ { 3 } , \ldots\) is defined by
$$\begin{aligned}
a _ { 1 } & = 2
a _ { n + 1 } & = 3 a _ { n } - c
\end{aligned}$$
where \(c\) is a constant.
- Find an expression for \(a _ { 2 }\) in terms of \(c\).
Given that \(\sum _ { i = 1 } ^ { 3 } a _ { i } = 0\)
- find the value of \(c\).