Answer:
40 units
Explanation:
An octagon is a polygon with 8 sides. A regular octagon is an octagon in which all their sides and angles are equal to each other.
Since the vertices of a regular octagon are located at (1, 4) and (4,8), hence the length of the side is gotten using the formula for calculating the distance between two points
.

Hence:

Since all the sides of a regular octagon are equal, therefore:
Perimeter = 8 × length = 8 × 5 = 40 units