buffer transformer
RMS is the equivalent DC value for an AC signal.
i.e. A sinusiodal voltage with amplitude 339.41V has an RMS value of 240V
So your answer is 240V.
Briefly how it the RMS of a signal is found is:
1. Signal is squared (so that average is not zero)
2. Squared signal is averaged
3. Squared averaged signal is square rooted, in order to get the non zero "average" (for a non biased ac signal, the average in the true sense of the word is zero), or DC equivalent, hence RMS (Root Mean Square).
For a sinusoid, the relation between the amplitude and RMS is sqrt2 i.e. RMS = Vpeak / 1.4142
Look for RMS definitions on the net for a more detailed explanation.