Answer
$9\times10^{16}e^-$
Work Step by Step
Find the number of electrons from the dose, the mass of the beef, and the energy per electron.
$$(4.5\times10^3Gy)(\frac{J/kg}{Gy})(5\;kg)(\frac{MeV}{1.60\times10^{-13}J})(\frac{1\;e^-}{1.6\;MeV})$$
$$=8.78\times10^{16}e^-\approx 9\times10^{16}e^-$$