Consider a closed-loop control system with a negative unity feedback and the open-loop transfer function below \((k>0)\). If the settling time of the system for the large \(k\) is about eight seconds, determine the value of parameter \(a\).

1) 1 2) 2 3) 3 4) 4

G(s) = k(s+4) s(s+2)(s+a)