Finding Feedback Resistance of Op Amp
I'll give you a hint here. You can calculate the Thevenin equivalent of the what is seen looking into R2. 

By inspection its source resistance is:

\$R_T =  R_2+(R_3||R_4)\$, and the open-circuit source voltage is:

\$V_{OUT}\cdot \frac {R_3}{R_3+R_4} \$

So the gain from the (virtual) Thevenin source is just -Rt/R1, but the output voltage must be higher by a factor of  \$\frac {R_3+R_4}{R_3} \$.

You can then calculate the gain and the output voltage. Chances are if this is actually built the op-amp will saturate at the negative rail. 

There are other, more general, ways to solve a problem like this (write the equations out) but with this way the answer drops out pretty easily.