1. We only consider the integral lengths.
So the pairs are simply the factors of 18:
1ft * 18ft, 2ft * 9ft, 3ft * 6ft
2. We simply get the factors.
3. We let the width be x so:
Area = length * width
18 = (x+8)x
4. It is a quadratic equation when simplified.
5. Yes, we just have to extract the roots.