#### Answer

Width = 7
Length = 2 x 7 = 14

#### Work Step by Step

Perimeter = 2(length + width)
Perimeter = 42 meters
Length = 2width (given)
Replacing in formula
Perimeter = 2((2w) + w)
42 = 2( 3w)
$\frac{42}{2}$ = 3w
21 = 3w
$\frac{21}{3}$ = width
Width = 7
Length = 2 x 7 = 14