${\rm What \ are \ the \ dimensions \ of \ velocity?}$

${\rm Given}$ $E=mc^2,$ ${\rm which \ of \ the \ below \ is \ the \ equivalent \ unit \ for \ the \ Joule?}$

${\rm The \ Boltzmann \ constant, \ } k_b {\rm \ is \ defined \ as \ } k_b = \frac{R}{N_0}, {\rm \ where \ } R {\rm \ is \ the \ gas \ constant \ with \ units \ Jmol^{-1}K^{-1}, \ and \ }$ $N_0 {\rm \ is \ Avagadro's \ constant \ with \ unit \ mol^{-1}. \ Using \ this \ information, \ what \ are \ the \ units \ of } \ k_b?$

${\rm The \ Coulomb \ constant \ is \ defined \ as \ } k = \frac{1}{4\pi\epsilon_0} {\rm What \ is \ the \ value \ of \ } \ k?$

$\epsilon_0=8.85 {\rm \ x \ }10^{-12} {\rm \ C^2N^{-1}m^{-2} }$

${\rm Given \ } \rho = \frac{m}{V} {\rm \ what \ are \ the \ units \ of \ } \rho {\rm?}$