From the statement of the problem, we know that the perimeter of the hexagon in the figure is:
The perimeter is equal to the sum of the lengths of the sides. So each side of the hexagon has a length:
The triangle inscribed in the hexagon is equilateral, so its three sides are equal. We see that the side AB of the triangle is also a side of the hexagon, so we have:
The perimeter of the triangle is equal to the sum of the lengths of its sides, so:
Answer
The perimeter of △ABC is 15.