In that case, you do have enough information. A proper meter measures RMS which I presume what you mean by Veff. Counting the number of squares on an oscilloscope will give the peak to peak voltage, which, assuming a symmetrical waveform, is twice the peak voltage.
For a sine wave: Vpeak = root(2)*VRMS
In an AC circuit, the total voltage is equal to the phasor sum of the voltage across the resistor (the real part) and the inductors and capacitors (imaginary). The voltage across the capacitor will be out of phase with the voltage across the inductor so it will cancel it out.
V = root(VR2+(VL - VC)2)