An electron drops from the 4th energy level in an atom to the 3rd
level and then to the 1st.  Two frequencies of light are emitted. How
does their combined energy compare with the energy of a single
frequency that would have been emitted if the electron had dropped
from the 4th level directly to the 1st?

I think that the sum of the energies of the two spectral lines in the
two-step case should equal the energy emitted in the single step case.