Hi there!
Let the width of the rectangle be called x. Then the length of the rectangle is 2x. We get the following perimeter:
[tex]x + x + 2x + 2x = 126[/tex]
Collect the terms
[tex]6x = 126[/tex]
Divide by 6
[tex]x = 126 \div 6 = 21[/tex]
Therefore, the width of the rectangle is 21 feet and the length is 2 × 21 = 42 feet.