The following circuit uses an ideal op-amp. Assuming that Vin = 6.2 mV, R1 = 2 k, R2 = R4 = 22 k, and R3 = 7 k, find the current I4 in microamps.
a) 0.28 µA
b) 0.62 µA
c) 1.12 µA
d) 2.54 µA