The formula for perimeter is P = 2L + 2W. We are told that the perimeter is 8 times the width, so P = 8w. We are also told that the length is 90. So our revised formula is 8w = 2(90)+2w, which simplifies to 8w = 180 + 2w, and 6w = 180. That means that w = 30. And there you go!
