Question 1150376
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<pre>

The area of the uncovered floor = (9+2x)*(12+2x) - 9*12 = 4x^2 + 42x.


The equation to find the uniform strip width is


    4x^2 + 42x = 270  square meters,  or


    4x^2 + 42x - 270 = 0.


    {{{x[1,2]}}} = {{{(-42 +- sqrt((-42)^2 + 4*4*270))/(2*4)}}} = {{{(-42 +- 78)/8}}}.


Only positive root  x = {{{(-42 + 78)/8}}} = 4.5  makes sense.


<U>ANSWER</U>.  The uniform width of the strip is 4.5 meters.
</pre>

Solved.


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Thanks to @MathTherapy (!)