Question 503498
Borders are interesting because you have to remember that you have to pave the 4 corners.
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The area of the garden = 12*16 = 192 square meters.
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Then you add the border with width 'x'.
So,
Length is now L + 2x
Width is now W + 2x
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We are told:
(L+2x)(W+2x) = 285 
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(12+2x)(16+2x) = 285
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192 +24x +32x +4x^2 = 285
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4x^2 + 56x + 192 = 285
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4x^2 + 56x - 93 = 0
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*[invoke quadratic "x", 4, 56, -93 ]
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You cannot have a negative width, so the border is 1.5 m.
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Always check your work.
L = 12 + 2(1.5) = 15
W = 16 + 2(1.5) = 19
15*19 = 285
Correct.
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Answer:  The border is 1.5 meters wide.
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Done.