Be careful that you define your variables consistently throughout your work.
Your original diagram appears to define I_U as the current flowing downward through the voltage source.
The symbol you are using for a voltage source is non-standard in my part of the world (I know that it is common in some places). Which is the positive terminal? The tip of the arrow or the tail? I'm guessing the tail.
But your notation on Circuit A indicates that I'_U is the current flowing downward through R4.
Circuit A is just a circuit to be analyzed. What do you get for your three variables of interest for it? Show your work!
Circuit B is just a circuit to be analyzed. What do you get for your three variables of interest for it? Show your work!
What do you get if you add the corresponding variables together?
by Kate Smith
by Jake Hertz
by Ikimi .O