Inverting Op-Amp Circuit Problem
Redraw the circuit like this







simulate this circuit &ndash; Schematic created using CircuitLab

The questions you have are essentially the same as finding the voltage at point a and b.

You worked question a correctly.

Now you can easily find out the current through R3 and use Ohm's law to find the drop across it. From the known voltage at a and the drop across R3, you can find the voltage at b.

Alternately, you know the voltage at the op-amp inverting input, and you can use the voltage drop across R2 to find V(b).