Answer:
x represents the width of the bookcase.
Explanation:
Let w be the width of the bookcase.
Bookcase that is 2 feet taller than it is width.
Length = w+2 feet.
Length of a board that can be cut for the top bottom 2 shelves and 2 sides of the bookcase.
Top and bottom = w+w = 2w
2 shelves = w+w = 2w
2 sides of the bookcase = 2(w+2)
Total length of a board that can be cut for the top bottom 2 shelves and 2 sides of the bookcase is
...(i)
It is given that total length of a board that can be cut for the top bottom 2 shelves and 2 sides of the bookcase is
...(ii)
From (i) and (ii) we get

Therefore, x represents the width of the bookcase.