l (length)=3x
P (perimeter)= 8x+6 = 2 x length + 2 x width
8x+6 = 2 (3x) + 2 x width
8x+6 = 6x + 2 x width
2 x width = 8x+6 - 6x
2 x width = 2x+6
width = 1/2(2x+6) = x + 3
Hope it helps
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