Make a figure and call x the width of the path.
The length and width of the combined rectangle are (31 + 2x) and (26 + 2x) respectively.
The area of this rectangle is (31 + 2x)(26 + 2x) = 1800
Expand this expression and collect terms to get:
The quadratic formula gives and extraneous root and x = 7.
You should put this answer back into the original problemt to be sure it is correct.