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

Problem 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!)
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##
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?

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