Again

(b) We have

Thus:

But as you know by http://www.mathhelpforum.com/math-he...ped-again.htmlwe have

Thus:

(c) Hint: Multiply the DSGF of

(a) Consider the different cases

(d) Use part (a) and the definition of (see whether our function is multiplicative) or use the series in (b) and remember/prove that