Let the length of rectangle is l and width is w …

Then according to the question ..

l = 2w..

Given..

Perimeter = 36 unit

We know that –

Perimeter = 2( lenth + width)

And l = 2w then..

36 = 2( 2w + w)

3w = 18

W = 6 and

l = 2*6

l= 12

Then lenth of rectangle of will be 12 and width of rectangle will be 6.