Question 1078267
x, the edge length of the square to remove


{{{(10-2x)(14-2x)=80}}}

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{{{2*2*(5-x)(7-x)=2*2*20}}}

{{{(5-x)(7-x)=20}}}

{{{35-12x+x^2=20}}}

{{{x^2-12x+15=0}}}

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{{{x=(12+- sqrt(144-4*15))/2}}}


{{{x=(12+- sqrt(144-60))/2}}}


{{{x=(12+- sqrt(12*7))/2}}}


{{{x=(12+- 2sqrt(21))/2}}}

{{{highlight(x=6-sqrt(21))}}}


About 1.42 inches