Use Block diagram algebra. See attached file for full problem description.
Denote the node before the block A (input to A) as "P".
Denote the node between the two summation points (input to the third summation point) as "Q".
We can then write down the equations:
P = R + QB + ...
A block diagram proble is solved. The solution is detailed and well presented. The response received a rating of "5/5" from the student who originally posted the question.