Check the picture below.
now, to get how much is the area of the tiled section, we simply get the area of the whole pool, 53x26, which includes the tiles, and then subtract the area without the tile, the rectangle in the middle, and what's leftover, is the area of the tiled area.

28: 1, 2, 4, 7, 14, 28
40: 1, 2, 4, 5, 8, 10, 20, 40
The common factors are 1, 2, and 4.
You can use a factor rainbow to help you find the factors (:
The answer is 3 1/3 + 2 1/3 = 5 2/3