The sum of length and width of a rectangle is half the perimeter. Here the sum of length and width is 114/2 = 57 ft.
If we add 12 ft to this total, we have a value that is 3 times the width.
The width of the sign is 69 ft/3 = 23 ft.
The length of the sign is (2·23 -12) = 34 ft.
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From the problem statement, using L and W for length and width:
... L = 2W -12
... P = 114 = 2(L +W)
Dividing the second equation by 2 and substituting for L, we have ...
... 57 = (2W -12) +W
... 69 = 3W . . . . . . . . add 12
... 23 = W . . . . . . . . . divide by 3
