Final answer:
The question involves using Stokes' theorem to convert a line integral of a vector field over a closed curve into an equivalent surface integral over the surface bounded by the curve.
Step-by-step explanation:
The subject of the question is the application of Stokes' theorem to evaluate a line integral over a vector field f = (x²+z) i + (4x + y) j + (9y − z) k. Stokes' theorem relates a line integral around a closed curve C, to a surface integral over a surface bounded by C.
In this case, C is the intersection of the plane x + 3y + z = 6 with the coordinate planes. The orientation of C is counterclockwise when viewed from above, which dictates the direction in which the surface integral should be computed. To use Stokes' theorem, we first need to find a vector field whose curl is f and then evaluate the surface integral of this curl over a surface bounded by C.