Question 1135914
2L + 2W = Perimeter
2L + 2W = 84
and we have that:
L = 2W + 6
Rewrite substituting for L:
2(2W + 6) + 2W = 84
4W + 12 + 2W = 84
6W = 72
W = 12 
So now we know that the width is 12. Let's find the length:
L = 2W + 6
L = 2(12) + 6 
L = 24 +6 = 30 
The length is 30
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Check:
2L + 2W = 84
2(30) + 2(12) = 84
60 + 24 = 84 Correct