We need to visualize the box by using a diagram attached with this problem.
[tex] Length = 14 \; feet [/tex]
[tex] Width = 20 \; feet [/tex]
[tex] Height = 8 \; feet [/tex]
The blue is smaller rectangle and brown is the larger rectangle
Conclusion:
Length of smaller wall (in blue color) is 14 feet
Width of smaller wall (in blue color) is 8 feet
Length of Larger wall (in brown color) is 20 feet
Width of the Larger wall (in brown color) is 8 feet
