Hi Pete

I do publish the derivations that the book cites (the H(z) stuff). But, the publisher did not do a homework solutions manual (they do this for some topics). Typically, the course instructor (professor) will help with the homework. But, if you are studying alone, then I can certainly help. 

The point of the second question is to help you flush out a difference equation from any block diagram. The sequence of steps to follow is on page 252 (section 10.23.3) and there are three steps (below is not verbatim, just another variation):

1) form y(n) first -- you do this by looking at y(n) and figuring out what you need to calculate it. Looking at Figure 10.49, you can see that y(n) is the output of a summer (top right of figure). The two input to that summer are in the storage registers. Read those out and form y(n).

2) check for underflow (there is a function for that and is documented in the book)

3) update state variables; this may only be done after y(n) is calculated and this is the most common mistake I see from students.

If you find yourself going around in circles, then stop and follow the 3 steps. 

LMK if you need some more help - trying not to just give you the solution (yet) but I will post that code if you want it. 

Will