Step-by-step explanation:
Let W=width of the garden.
Then length of the garden is W+12.
Area of the garden = W(W+12) = 108.....................(1)
rearrange (1)
W^2+12W-108 = 0...................(2)
Factor (2) [ 108 = 3^3*2^2 = 8*12 = 6*18 = ...]
W^2+12W-108 = W^2+18W - 6W -6*18 = W(W+18)-6(W-18) = (W+18)(W-6) = 0
Therefore W=-18, or W=6.
Rejecting negative roots, W=6, therefore length, L = 6+12 = 18
Answer: The garden measures 18' by 6'.