Let's use the variable x to represent the length of the first and second pieces.
If the third piece has twice the length of the first and second, its length is 2x.
If the fourth piece has half the length of the first and second, its length is 0.5*x.
Adding all four pieces and equating to 54 inches, we have:
So the length of each piece is:
12 inches, 12 inches, 24 inches and 6 inches.