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put this solution on YOUR website!(30+2X)(40+2X)=1800
1200+80X+60X+4X^2=1800
4X^2+140X+1200-1800=0
4X^2+140X-600=0
X^2+35X-150=0 USING THE QUADRATIC EQUATION WE GET:
X=(-35+-SQRT[35^2-4*1*-150])/2*1
X=(-35+-SQRT[1225+600])/2
X=(-35+-SQRT1825)/2
X=(-35+-42.72)/2
X=(-35+42.72)/2
X=7.72/2
X=3.86 ANSWER FOR THE BORDER.
PROOF
(30+2*3.86)(40+2*3.86)=1800
(30+7.72)(40+7.72)=1800
37.72*47.72=1800
1800=1800