Question 1145565
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<pre>
Let w be the frame uniform width.


Then your setup equation is this


    {{{(10.5+2w)/(14+2w)}}} = {{{5/6}}}.


To solve it, cross multiply


    6*(10.5 + 2w) = 5*(14 + 2w).


The rest is several easy steps

    
     63 + 12w = 70 + 10w,

     12w - 10w = 70 - 63

      2w       = 7

       w       = 7/2 = 3.5 inches.      <U>ANSWER</U>


Then the outer dimensions of the frame are 10.5+2*3.5 = 17.5 inches and 14+2*3.5 = 21 inches.    <U>ANSWER</U>


<U>CHECK</U>.  The ratio of outer dimensions of the frame is  {{{17.5/21}}} = {{{5/6}}}.   ! Correct !
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Solved.