Evaluate the surface integral ffxyz) f(x,y,z) dS using an explicit representation of the surface. f(x,y,z) = e; S is the plane z = 12-x-3y in the first octant. Set up the surface integral for the given function f(x,y,z) over the given surface S. Integrate with respect to x first. Use increasing limits of integration. f(x,y,z) ds = ) dx dy SE (Type exact answers.)