NascentOxygen,
Zc = (Zb * Zd) / Za
Zc = (3k * 12k) / 5k
Zc = 7.2k
These values would balance the circuit (Vx=Vy).BvU,
Sorry, but I don't fully understand #12. Apologies for my poor knowledge, I'm a long way from my comfort zone with this and the material from my Uni doesn't seem...