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(b) Consider a fluid with density M ( X, y, Z ) = 1 + x2 + 12 measured in g/in' flowing with velocity U(x, y, Z) = (x, y, 1) measured in in/s. The net amount of fluid that goes through M per unit of time (in this problem, per second) in a specified direction (one of two possible orientations for M) is referred to as the mass flow rate of the fluid through M. It is given by the surface integral MU . Nas, M where N denotes a normal field to M compatible with the orientation we are interested in. Show that the net amount of fluid that passes through our surface M going down after 4/3 seconds is W/ A MU . N dS = (1 - log(2))n M grams. Here, "going down" means that we choose an orientation for M so N is a downward normal vector. (c) Notice that the quantity you found in (b) is positive. From a physical perspective, what is the meaning of the positive sign in this computation? Use a single sentence to answer this