Ahydrogen atom emits a photon of wavelength 1879 nm. from what energy orbit to what lower energy orbit did the electron jump?

The frequency of the emitted photon is given by:

where
is the speed of light

So we find


And the energy of the emitted photon is given by

where  is the Planck constant
f is the frequency
Substituting, we find


If we convert this into electronvolts:


This is the amount of energy lost by the electron in the orbit transition. If we have a look at the values of the orbit energy in the hydrogen atom:
https://i.stack.imgur.com/6raba.jpg
We can see that this difference of energy corresponds to the transition between the orbit n=4 (-0.85 eV) to the orbit n=3 (-1.51 eV):