Question 1111014
The Cardboard
Width x
Tall x+25
Area of this carboard  {{{x(x+25)}}}


Total area of border plus carboard
{{{(x+2*5)(x+25+2*5)}}}
{{{(x+10)(x+35)}}}


Area of JUST THE BORDER
{{{highlight_green((x+10)(x+35)-x(x+25)=1350)}}}

-

{{{x^2+45x+350-x^2-25x=1350}}}
{{{45x+350-25x=1350}}}
{{{20x=1350-350}}}
{{{20x=1000}}}
{{{2x=100}}}
{{{highlight(x=50)}}}------width
-
Height is {{{highlight(75)}}}.