The question doesn't make much sense!
It is at resonance and that means:
1) Xl = Xc
2) Supply voltage and current are in phase
3) Supply voltage is the voltage across R
4) The power is dissipated in R
This means that you can calculate the value of R. You are given the resonant frequency so you can calculate Xc and therefore Xl.
I don't understand what they are asking !!!!
The problem asks about the energy stored in the inductor and in the capacitor, when the current is zero, so the voltage across the reactive elements is of maximum magnitude. You need the formula for the energy stored in an inductor and in a capacitor.
t=0 does not mean that the source was switched on at that instant. The generator voltage has been the same before we started to measure time.