It is actually the exam of 2018-02-14, problem 6c (please make this more precise in future questions; it takes time to find the exercise problems otherwise).
The mentioned state s4 is actually the state s1' introduced in part a). It seems that it had been renamed to use the teaching tool; I will rename it to s1' for better understanding.
The exercise instructs you to apply the Rabin-Scott construction to the automaton obtained in part a). It does not say that this automaton is equivalent or whatever. So, just applying the Rabin-Scott construction you obtain the above automaton. The automaton of part a) had as single accepting state s1' (or s4) and that leads to the above solution.
