Question

The temperature and pressure in the Sun's atmosphereare2.00x10⁶K and .0300 P_a. Calculate thermsspeed of free electrons (mass 9.11x10^-31Kg)there,assuming they are an ideal gas.

This is question 19-22 in Fundamentals of Physics by JearlWalker8th edition. I understand everything except how they got M.Theysay M is m*N_a, but how did they getN_a?

Thanks so much!