Answer:
(40 + 2x)feet
Step-by-step explanation:
see attachment for the figure.
Let 'L' represents the length of the rectangular swimming pool i.e 40ft wide.
and pool is bordered by square tiles that are x feet in length surrounding the pool
therefore,
In order to find the longest side of the pool and the tile border, take the sum of Ā length of the swimming pool i.e 40 adding two times the wide of the square tiles
(40+2x)feet.