Spectral lines and energy levels

[Pika007]

Homework Statement

In the spectrum depicted bellow (see added picture) are spectral lines which resulted from emissions of a photon due to an electron decaying from a higher to a lower orbital in a Hydrogen-like atom (meaning- only one electron. No details about the nucleus)
All lines in the given spectrum are a result of an electron decaying for an excited state to the first excited state. The wavelength of line C is 48.214nm, Calculate the energy of a photon co-responding to line D.

Homework Equations

v=c/f
E(ph)= hv
Reidberg's equation (too complicated to type in)

The Attempt at a Solution

Our presentation didn't include any similar example, so I'm at a loss about how to approach this. Been staring at the page for a better part of the day.
Any help would be much appreciated

 

[kontejnjer]

The Rydberg formula for hydrogen-like atoms is:
$\frac{1}{\lambda}=RZ^{2}(\frac{1}{n^{2}_f}-\frac{1}{n^{2}_i})$
Since the graph constitutes the entire spectrum for any $n_i\rightarrow2$ transition with $n_i>2$, where $n_f=2$ for any transition (since $n=2$ for the first excited state).
Notice that A corresponds to transition $3\rightarrow2$, B corresponds to $4\rightarrow2$ and so on, hence you can figure out which transitions correspond to lines C and D respectively.

 

[Pika007]

ok, this clarified some things up, especially explaining the transitions.

EDIT-
thanks, i got it. Also managed to understand things properly along the way.