We assume R-Phase and Y-Phase are measured relative to the Neutral ground icon.
The influence of the resistor network is symmetrical.
Therefore V is always the average of R-Phase and Y-Phase.
Perhaps the answer requires more thought than the above, so don't take my reply as the only answer.
R1 does not figure in this problem. So using the red phase as a reference, add to it another 230V @120 degrees. answer as above. More accurate answer is 415/3^-2 instead of 230V.
Frank