You are told that the length of the pool is represented by x+14. Dividing the volume (x^3 + 16x^2 + 13x - 210) by x+14 leaves you with x^2 +2x - 15, which represents the area of a cross section of the pool perpendicular to its length.
I used synthetic division with -14 as my first divisor; the result was 1 2 -15, which represents x^2 + 2 - 15. This x^2 + 2 - 15 is easily factored (try using 3 as divisor in synthetic division); the factors are x-3 and x+5.
These results represent the width and the depth of the pool, not necessarily in that order. However, the width is likely to be greater than the depth, so I would conclude that the width is x+5 and the depth is x-3.
