Refer to the problem documented here: https://www.circuitlab.com/circuit/cju6v8/practice-problem-5_3/ Assume idea op-amp. The textbook is Fundamentals of Electric Circuits by Charles Alexander and Matthew Sadiku. The textbook answer for the current through the feedback is 26.25uA. I'm stumpped as to how they get this. For vo, I get -3.15V just like the text. By hand, I get 3.15 v / 280,000 kOhm = 11.25uA. This is the same answer I get from Circuit Lab.