Related to theory of Automata

             Question 1:
           a)   Determine which of the following sets have valid / invalid alphabets:
           1 = {a, ab, b, d, ae}
             2 = {a, ba, c, d}

        b)  Consider  = {ab, baa, c, db} to find the length of the string s=abbaaabdbbaa by tokenizing. Give its reverse Rev (s).

         Question 2:
          a)    Give the regular expression RE over  = {a, b} for the language of all words having b as a second letter. 

       b)   What will be the Finite Automata for above language?