Assume it's width is x. The length, which is twice as long, is then 2x.
The perimeter consists of two sides that are the width, and the other two which are length, so you multiply both the width and length by two and add the products to get the perimeter. So if the perimeter is 216 yards:
2*x+2*2x=216, or 2x+4x=216
6x=216, so x=36. Twice that is 2*36=72.
The width is 36 and length is 72.
