L= length
W= width= 9 yards
Perimeter= 72 yards
Plug in the numbers you know and solve for L.
Perimeter= 2L + 2W
72= 2L + 2(9)
72= 2L + 18
subtract 18 from both sides
54= 2L
divide both sides by 2
27= L
CHECK:
72= 2(27) + 2(9)
72= 54 + 18
72= 72
ANSWER: The length is 27 yards
Hope this helps! :)