.
Equation (B) y = - x + 30.25 is equivalent to
x + y = 30.25
which describes the sum of the length and the width as half of the perimeter,
so this equation is good and relevant to the problem.
Three other equations, (A), (C) and (D) are irrelevant.
In my view, this method of teaching, giving irrelevant questions for discussion,
educationally is very bad and methodologically is inacceptable.
It only causes disgust.
If a person gives such assignments to students, it only means two things:
(1) this person can not teach, at all,
and
(2) this person is not ready to teach.
It is better to keep such a person at a cannon shot’s distance from teaching.
Also, I would not have objections, if somebody will come with the idea to double this distance.