The formula S A equals 2 left parenthesis l h plus l w plus w h right parenthesis gives SA, the surface area of a rectangular prism with length l, width w, and height h. For a rectangular prism with surface area 256 square centimeters, height 5 centimeters, and width 4 centimeters, the formula becomes 256 equals 2 left parenthesis 5 l plus 4 l plus 5 times 4 right parenthesis. What is one half of the length of the prism?