ANSWER:
120 feet
STEP-BY-STEP EXPLANATION:
We hve the following:
A = 10800 ft²
w = 90 ft
The area of a rectangle is the product between the length and the width, we do not know the length but we do know the area, therefore, we calculate the length as follows:
[tex]\begin{gathered} A=w\cdot l \\ \\ \text{ We replacing} \\ \\ 10800=90\cdot l \\ \\ l=\frac{10800}{90} \\ \\ l=120\text{ ft} \end{gathered}[/tex]The length of your backyard is equal to 120 feet