Inverting Op Amp question
There is an easier way to think about this problem, assuming ideal components. First, since the noninverting pin is grounded, the inverting pin is at virtual ground. This means:

\$V_{R1}=V_{in}\$.

\$\therefore I_{R1}=I_{R2\parallel R4}=I_{R3}\$

Calculate the voltage drop across \$R_{2\parallel 4}\$ in series with \$R_3\$, and you'll arrive at \$V_o\$ from there.