Question 759002
The area of a rectangle is 96ft square. 
The width is 4 less than the length. 
What is the perimeter? 

I am having trouble coming up with a formula for questions similar to this.  
L*W = 96,   and L-4=W  is all I got.
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That's all you need.
Sub for W in the 1st eqn
L*W = 96
L*(L-4) = 96
L^2 - 4L - 96 = 0
(L - 12)*(L + 8) = 0
L = 12
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W = 8
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You could have tried factors of 96 and gotten 8 by 12, too.
Perimeter = 40