Problem Solving (PS) | Re: In the x- y plane, there are 4 points (0,0), (0,4), (6,4), and (6,0).

I am too, having a problem comprehending this question.
If x+y < 4, why the area included (4, 0) & (0, 4) ?
I'm quite sure you meant x+y <= 4, otherwise, we cannot calculate this using areas.

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