Start by setting up the standard equation for perimeter of a parallelogram, P=2w+2h (these variables of course being width and height).
Now, substitute in what you know...
The problem tells us that width is equal to height minus four. This means that, in order to keep only one variable in this problem, we will write width as h-4.
The problem also tells us that 72 is the perimeter, so we substitute that for P.
72=2(h-4)+2h
Now solve from here.
(Distribute first)
72=2h-8+2h
(Combine like terms)
72=4h-8
80=4h
(Isolate h)
80/4=h
20=h
Now we know that the height is 20 meters. This means that the width, being four less than the height, is 16 meters.
Hope this helps! Good luck.