Question

how to find an unknown measure of the rectangle if the perimeter is 54 how they got 54

Answer 1

Well, based on the information that you gave me, I found that the measurements could be 12, 12, 15, and 15. because when you add them up, you get 54.
plz dont report, u didnt give enough info, so i tried my best.

Answer 2

They got 54 by measuring the length of each side
and then adding up the lengths of all the sides.