B. 8ft
Explanation:
The formula for the area of a rectangle:
[tex]\text{width }\cdot\text{ length = Area}[/tex]Since the width here is twice the length => width = 2* length
Let's say that length = x
=> width = 2x
Formula
[tex]\begin{gathered} \text{Area = }x\cdot2x \\ 128\text{ = x }\cdot2x \\ 128\text{ =}2x^2 \\ 2x^2=128 \\ x^2=64 \\ x=8\text{ or -8} \end{gathered}[/tex]Since the measure can only be positive the length is 8 ft long
