Answer: There are 4 rolls she should buy.
Step-by-step 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 ":
[tex]Area=2(l+b)h\\\\Area=2(9+11)\times 8\\\\Area=2\times 20\times 8\\\\Area=320\ ft^2[/tex]
Area of each single roll covers = 72 square feet
So, Number of single rolls of wallpaper is given by
[tex]\frac{\text{ Area of 4 walls}}{\text{ Area of single roll}}\\\\=\frac{320}{72}\\\\=4.44\\\\=4[/tex]
Hence, there are 4 rolls she should buy.