Charge-to-mass ratio with Zeeman Effect

[tuomas22]

Homework Statement

I'm supposed to determine e/m using Zeeman effect.
B=0.45 T
Difference between two spectral lines is also known (0.649x10^10 Hz)

Homework Equations

Normal or anomalous Zeeman effect? How you know it?
I'm guessing normal, so
\Delta E = m_{l} \frac{e \hbar}{2m_{e}}B

\Delta E = h \Delta f

so,

\frac{e}{m_{e}} = \frac{h \Delta f2m_{e}}{m_{l} \hbar B}

The Attempt at a Solution

Well the attempt at solution is the equations I just wrote, are they right so far?

But the problem is, how I get m_{l}? I think it's 2l+1, but how I get l from the know data then?

 

[tuomas22]

any tip would be much appreciated, I got exam tomorrow and I want to understand this :P