(I) is cubic i think
strings are of the form aa....(b or c)* ab c*
now ab has to be present in all strings....so given at string of length N, we have only N-2 places to be filled by the other three elements i.e either a* , (b or c)* , c*
this could be done in
(N-2-2) a's, b, c or (N-2-2) a's ,c,c --- 2 ways
(N-2-3)a's,bb,c or (N-2-3) a's,b,cc or (N-2-3) a's,c,cc -- 3 ways
(N-2-4) ... --------------- 4 ways and so on.
This is of the order of (N-2)*{(N-2)*(N-2+1)/2} ---> Cubic.
(II) is linear.
it allows only string of the form abc* which is a linear growth.