So this whole integral (let me rewrite it) of F.n ds tells us the mass exiting the curve per second and this should also be consistent in the last video we saw that this is equivalent to- and this is where we kinda view it as a 2-dimensional divergence theorem in the last video, we saw that this is equivalent to the double integral over the area of the divergence of f which is essentially just- well, I could write it 2 ways the divergence of f and this right over here, that's just the partial of the i component with respect to x (let me write it over here, I don't want to do this too fast and loose) so this right over here is going to be the partial of Rho M (let me write it like this), Rho M with respect to x plus the partial of the y component