Picture four long pieces. One piece is 5" long, the next is 6" long, the next is 7" long and the last one is 8" long. If you see each piece has 5" (like the first one) but 1 or 2 or 3 more inches, then add them in your mind as: 5" and 5 & 1 (6)" and 5 & 2 (7) " and 5 & 3 (8)" makes 5 & 6 & 7 & 8=26" long.