Well, what are the units of this going to be right over here? we know what Rho M is- Rho M gives us kilogram per meter second but if we take the derivative with respect to meters again, the units for either of these characters are going to be kilograms per meter second per second because we're taking the derivative with respect - sorry per METER, we're taking the derivative with respect to another unit of distance so you're going to take per meter so you're going to have another meter right in the denominator that's going to be the units here and then you're multiplying it times an area so that would be meters squared, this right over here is square meters they cancel it out, and once again this whole part here that you're summing up gives us kilograms per second, so you're having a bunch of kilograms per second and you're just adding them up throughout the entire area right over here