(a) Design an ideal inverting summing amplifier to produce an output voltage of \(v_{O}=-2.5\left(1.2 v_{I 1}+2.5 v_{I 2}+0.25 v_{I 3}\right)\). Design the circuit to produce the largest possible input resistance, assuming the largest resistance in the circuit is limited to \(400 \mathrm{k} \Omega\).

(b) Using the results of part (a), determine the current in the feedback resistor for \(v_{I 1}=-1.0 \mathrm{~V}, v_{I 2}=+0.25 \mathrm{~V}\), and \(v_{I 3}=+2 \mathrm{~V}\).