Area = Length x width
Area = 90 so we factor 90 and get 90 x 1; 45 x 2; 30 x 3; 22.5 x 4; 18 x 5; 15 x 6; 12.85 x 7; 11.25 x 8 and 9 x 10 or 10 x 9
All of these lengths (the first number) can be the length because it meets the equation. However, with out additional information I would think about what a pool looks like and decide it is either 9 or 10