.
From the context, the pen has 3 walls: one wall is parallel to the wall of the kennel
and two other walls are perpendicular to it.
The problem must say it directly and explicitly, but the problem's composer failed to do it, UNFORTUNATELY.
(Because he (or she) has no experience in formulating Math problems).
If x represents the width of the pen, then the length of the pen is (80-2x) meters.
It is the answer to the first question.
The area of the pen is the product of its width by its length
area = x*(80-2x) = -2x^2 + 80x.
It is the answer to the second question.
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All questions are answered and carefully explained.
The solution is complete.