The perimeter of a rectangle is eight times its width. if the length of the rectangle is 90 inches, what is its width in inches?

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!