The problem statement tells you the length of the first leg is "l".
The length of the second leg is l/2.
The length of the third leg is 2(l/2) -3 = l -3 ft.
The length of the three legs totals 32 ft
.. l +l/2 +(l -3 ft) = 32 ft
.. (5/2)l = 35 ft . . . . . . . . . combine like terms, add 3 ft
.. l = (2/5)*35 ft = 14 f
The length of the side of the shed is 14 ft.