What is the equivalent Boolean expression in product-of-sums form for the Karnaugh map given in fig?

Consider the circuit in Fig. Which has a four bit binary number $${b_3}\,{b_2}\,{b_1}\,{b_0}\,$$ as input and a five bit binary number $${d_3}\,{d_2}\,{d_1}\,{d_0}\,$$ as output. The circuit implements:

Consider the circuit in fig shown $$f$$ implements

Consider the synchronous sequential circuit in fig.

(a) Draw a state diagram which is implemented by the circuit. Use the following names for the states corresponding to the values of flip-flops as given below.

(b) Given that the initial state of the circuit is $${S_4},$$ identify the set of states which are not reachable.