Step-by-step explanation:
The area is
[tex] {x}^{2} - 110x + 2800 \\ = {x}^{2} - 40x - 70x + 2800 \\ = x(x - 40) - 70(x - 40) \\ = (x - 40)(x - 70)[/tex]
Since the width is
[tex]x - 40 \: (feet)[/tex]
Then, the length will be
[tex]x - 70 \: (feet)[/tex]
