If w=width of the porch then its length is 2w+3 so the perimeter is 2(2w+3+w)=54 if the lights go all round the porch. So 3w+3=27 (sum of length and width). Divide through by 3: w+1=9, so w=8 ft and length=2×8+3=19 ft. So the length is 19 ft and the width is 8 ft.