How to verify Stokes theorem on a triangular pyramid?

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I'm trying to solve a problem which is giving me some troubles, it's about applying Stokes' Theorem on the surface defined by:

$ x = 0, y = 0, z = 0 , (x + y + z) = 2 $

of the field

$ F = (x, -y, z) $

Whith the orientation n pointing towards the axis origin O.

The surface Σ should look like a triangular pyramid, with one of the vertices in the origin O. So I thought to just consider the pyramid face opposed to the vertex in O, so the one with the equation

$ (x + y + z) = 2 $

So i calculated

$ \int_{\delta (+) \sum }^{ } F * dr $

With Stokes' Theorem, considering

$ z = 2 - x - y $

and it returns

$ (\int_{0}^{2 - x}\int_{0}^{2} 2) = 4 $

So 4 or -4 depending on the orientation...

Then i'm requested to compute

$ \int_{\delta (+) \sum }^{ } F * dr $

with a direct method, using line integrals. Here comes my problem: how do I set the line integrals? Should I just consider

$ (x + y + z) = 2 $

or the other faces too?

I'm sorry for the bad English... thanks in advance!