Total surface area of a triangular prism = width x height +(sum of sides + width) x length 475 = (width x 10) + (5 + 5 + width) x 15 475 = (10 x width) + (10 + width) x 15 475 = (10 x width) + 150 + (15 x width) 475 - 150 = 25 x width 325 = 25 x width width = 325/25 = 13 feet