How to present the charges of quarks with the following Nc?

[HerrBlatt]

Homework Statement

Assume that quarks are presented in SU(Nc) with a unknown dimension of Nc, and define the rate Rμ of the scattering cross sections between e+e- -> hadrons(here, consider u, d, s, c, b quark) and e+e- -> μ+ μ-. Give out the result of Rμ with Nc. See detailed equations below.

Relevant Equations

Rμ = σ（e+e- -> hadrons）/ σ(e+e- -> μ+μ- )

I have already known the cross sections can be presented like this.
σ（e+e- -> hadrons）∝ Σ eq^2 & σ(e+e- -> μ+μ- ) ∝ e^2,
where eq is the charge of a certain quark(u, d, s, c or b)
But I don't know the relationship between Nc and eq.

(This is my first time to post a thread. I don't know how to insert a equation typed in LaTex or Word, so it may be a little tired to read...
I'm so sorry about that and thank you for help!)

 

[mfb]

What does the sum run over for hadrons? It is not just the flavor. How is that related to the symmetry group?

You can use LaTeX with ##. ##a^2## -> $a^2$

 

[HerrBlatt]

You mean it also runs over colors? And we should multiply a Nc on it? In this way the sum will be 11/9 Nc?

 

[mfb]

You mean it also runs over colors?

Right. More colors -> more hadrons.
I'm not sure where the 11/9 came from.