Question 1110877
x, the width
3x, the height


Just the post, area is  {{{3x^2}}}.


Five-inch border?
Combined width and height become  x+10 and 3x+10.
This COMBINED AREA is  {{{(x+10)(3x+10)}}}.


Area of JUST the border?  The border ONLY?

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Do you know what to do?