The width of the mural is 8ft... how'd I get that??? First , you need to know the formula for the area of a rectangle ... A = LxW. The length is 9 , so what number multiplied by 9 equals 72? 8! 9x8=72 . The perimeter equals 35 feet . How'd I get that??? The width and length should both be multiplied by 2 . 9x2=18 and 8x2=16 . 18+16=35 feet !