Commenting frequency spectrum of a sampled data
Consider the 3V component first (note that aliassing only affects frequency, not amplitude, so the 3V component will have the same magnitude at whatever frequencies it is aliassed to):

For Fs = 115 Hz the 3V component shows up at 2 Hz, so it's real frequency could be any value which satisfies f = 115*k +/- 2, i.e.

  2 Hz
113 Hz
117 Hz
228 Hz
232 Hz
...


Do the same thing for Fs = 280 Hz, where we have f = 280*k +/- 48:

 48 Hz
232 Hz
328 Hz
512 Hz
608 Hz
...


And then again for Fs = 500 Hz:

232 Hz
268 Hz
732 Hz
...


We can see that the only frequency which corresponds in all 3 cases is 232 Hz, so it looks like we have a 3V component at f = 232 Hz.

You can now apply the same approach to identify the frequency of the 1V component.