Theory:

Any figure with all the sides of equal length and all the angles of equal measure, then the figure is said to be regular closed shape.
We know that the perimeter of the square is $$4$$ times the side length of the square.

Similarly, the perimeter of the equilateral triangle is $$3$$ times the side length.

Since the square and the equilateral triangle have their sides of equal length and have an angle of the same measure, these shapes are said to be regular shape.

Thus, the perimeter of any regular shape is the product of the number of sides of the regular shape and its side length.
Example:
The side length of the regular heptagon is $$9$$ $$cm$$. Find the perimeter of the regular heptagon.

Solution:

The side length of the regular heptagon $$=9$$ $$cm$$

The number of sides of the regular heptagon $$=7$$

The perimeter of the regular heptagon $$=$$ Number of sides $$\times$$ side length

$$= 9 \times 7$$

$$= 63 \ cm$$

Therefore, the perimeter of the regular heptagon is $$63$$ $$cm$$.