Find resistors for an OP AMP
The problem's circuit won't work as shown, and I missed that the horizontal resistors in the "T" network are supposed to be equal, but if the opamp's supply is allowed to be bipolar, here's one way to get the circuit to work:


Select Vout to be a value close to the opamp's negative
supply,leaving enough headroom so the opamp's output won't be
clipped, say -20 volts.
Since the circuit inverts and its gain is to be -400, Vin must
be:


$$ Vin =\frac {-(-Vout)}{Av} = \frac {20V}{400} = 0.05V = 50\text { millivolts}$$ 


Since U1's non-inverting input (U1+) is grounded, U1- will be a
virtual ground, so pick a value for R1 which will drop 50 millivolts
with a decent amount of current through it, say 5 microamps. Then:


$$ R1 = \frac{Vin}{Iin} = \frac {50mV}{5\mu A} = 10k \text{ ohms}$$


With 5 microamps through R1 and with VIN equal to 50 millivolts,
you'll need a  current sink which can pull U1- down to zero volts.
One way to do it is to use another equal valued resistor (R2) which
will also drop 50 millivolts with the R2 R3 R4 (V4) junction at -50
millivolts. 

Since R1 and R2 are in series, and the current through R1 is 5
microamps, the current out of R2 must be -5 microamperes.
If the R2 R3 R4 junction is to sit at -50 millivolts, and the
resistance of R3 is chosen, arbitrarily, to be 10k ohms, then R3
must drop 50 millivolts and the current out of R3 and into the R2 R3
R4 junction must be -5 microamps.

Then, with Vout at -20 volts,


$$ R4 = \frac{Vout-V4}{I3} = \frac {(-20V)-(-50mV)}{10\mu A} = 1,995,000\Omega \approx 2  \text { megohms.} $$