Let
x----------------> <span>width of the margin
we know that
[Area </span><span>printed matter]=140
</span>[Area printed matter]=[(14-2x)*(18-2x)]
then
[(14-2x)*(18-2x)]=140--------> (252-28x-36x+4x²)=140
(252-64x+4x²)=140----------> 4x²-64x+112=0
using a graph tool---------> <span>I solve the quadratic equation
see the attached figure
x1=2
x2=14----------> is not solution
the answer is
the margin should be 2 cm</span>
x----------------> <span>width of the margin
we know that
[Area </span><span>printed matter]=140
</span>[Area printed matter]=[(14-2x)*(18-2x)]
then
[(14-2x)*(18-2x)]=140--------> (252-28x-36x+4x²)=140
(252-64x+4x²)=140----------> 4x²-64x+112=0
using a graph tool---------> <span>I solve the quadratic equation
see the attached figure
x1=2
x2=14----------> is not solution
the answer is
the margin should be 2 cm</span>