Answer:
20.7 yd(rounded)
21 yd (exact)
Explanation:
Since it goes 7 wide, do 7 x1/3 = 2.3 The 1/3rd comes from measurement given.
The length is 3 x 1/3 = 1 yd., so each level is 2.3 (repeating).
Since the height is 9, 9x2.3 = 20.7 yds (rounded)
If you want to be exact, 2.3333333333 x 9 = 21 (exact)