Hello.
The area of a square is calculated by the formula:
A = l²
As A = 75 ft², we have:
75 = l²
l = √75
Now, note that: 75 = 3 . 25 = 3 . 5²
So:
l = √(3 . 5²) = √3 . √(5²)
l = 5√3 ft
Now, we can assume √3 = 1.73
l ≈ 5 * 1.732
l ≈ 8,7 ft (Note that I have already put it in the nearest tenth)
OK :)