I'm looking for the reason why there is the number eight $8$ at the r.h.s. of EI:
$$R_{\mu\nu}-\frac{1}{2}Rg_{\mu\nu}=\frac{8\pi G}{c^2}T_{\mu\nu}.$$
My attempt was to take the limit of this equation to be Newton's equation and I considered 2 steps none of which is clear enough to me:
$$R_{00}\approx-\frac{\nabla^2\Phi}{c^2}=\frac{8\pi G}{c^4}\rho c^2$$ and my second unclear point is why after cancellation do we have
$$\nabla^2\Phi= 4\pi G \rho$$ and how this give us the number $8$ on the r.h.s. of EI above.
EDIT
in the link provided there is no explanation of the number $8$ on the r.h.s. of Einstein's Eq.
