The length of the pantry is 3 feet.
You start by dividing 81 by 9 since the pantry's area is 9 times the area of the whole kitchen. Then you divide the area of the pantry (which is 9 because 9 times 9 is 81) by 3 since length times width equals the area. You get 3 feet in the end.
Hope this helped :)
