As shown in the figures given :
For Figure 1 : perimeter = 8 units [As can be seen in the figure]
For figure 2(with 2 octagons) : perimeter = 8 × 2 - 1 = 15 units [since 1 side is common ]
For figure 2(with 3 octagons) : perimeter = 8 × 3 - 2 = 22 units [since 2 sides is common ]
If one more octagon is added
then perimeter = 8 × 4 - 3 = 29 units [since 3 sides will be common ]
