A mat is 3w inches wide and the frame is w inches wide around a 16in x 48 in poster. Type an expression for the amount of frame material needed.
you mean area, or length? If area, then
(16+6w+2w)(48+6w+2w)-(16+6w)(48+6w) = 28w^2 + 128w in^2
(16+6w+2w)(48+6w+2w)-(16+6w)(48+6w) = 28w^2 + 128w in^2