If the length is 20 feet, the other side must be 20 feet as well. The perimeter is the addition of all sides of a rectangle. Length: 20 on one side, 20 on other side. Subtract the length from total perimeter and you get 24 feet remaining. Divide 24 by 2. 12 feet for the width.
Take 19.95 and subtract 17.85 from it to get 2.10. Divide 2.10 by 19.95 to get 0.105. Multiply that by 100 and you get 10.52. So it's 10% or maybe 11% if you're supposed to round. Hope this helps
