I understand norton equivalent and I understand thevenin equivalent and how it can be used to simplify CIRCUIT A into CIRCUIT B. What I don't understand is my books explanation of simplifying CIRCUIT C into CIRCUIT D. They basically claim that Circuit B Vth is just the voltage division so that Vth=R2/(R1+R2)*(V+). I get that, and it works if you also convert (V+) and R1 into Norton equivalent, see that R1 is now parallel with R2 and combine then, and then convert the current source and Rth into Thevenin equivalent.
What I don't get is how they got Vth for Circuit D.
Norton Equivalent of V+:R1 and V-:R2
Parallel simplification of Inorton(1) and Inorton(2)
Parallel simplification of R1 and R2
Thevenin equivalent of Inorton and Rth to get Vth and Rth
Where am I going wrong. My solution is in the picture below for Circuit C.