Find the perimeter of 6 regular octagons linked together side by side, if one side is 4.5 inches. 


Six regular octagon arranged side to side is shown in the diagram below.

The shape has 38 equal sides, each side is 4.5 inches, so the perimeter is

4.5 × 38 = 171 inches

Check the picture below.

also notice, the octagons on either edge, include 7 sides to the perimeter, whilst the octagons in between, only include 6 sides to the perimeter.

so, add all sides, excluding those borders, and that's the perimeter.