Answer: There are 4 rolls she should buy.
Explanation:
Since we have given that
Length of wall = 9 feet
Width of wall = 11 feet
Height of wall = 8 feet
As we know the formula for "Area of four walls ":

Area of each single roll covers = 72 square feet
So, Number of single rolls of wallpaper is given by

Hence, there are 4 rolls she should buy.