Question 825456
The picture or diagram is not shown to us, but your fencing formula which I would not really call as "perimeter", is correct, indicating that x is one of the lengths of the divider as well as one of the dimensions of the whole rectangular form.  y is the other dimension of the whole rectangular form.


Your mistake only appears to be your area formulation.  This should be, {{{highlight_green(A=xy)}}};


From this, you may find no further trouble nor confusion.