Perimeter is adding all sides (Length(L) +width(W)) example rectangle is length + width but since it has 4 sides, it would be p=L+L+W+W or p=2L+2W For square it's p=L+L+L+L since L=W or p=4L
That table shows measurements (in invhes$ from cubes with different side lengths. which pairs of variables have a linear relationship? check all that apply